How do you call such chord?

[Passante]

A D C

A as a root note in the A Aeolian mode.

[The Noodlist]

A/D-7? D-7/A edit I've let my reading knowledge lapse.
A over D minor 7?
A-11?
https://www.scales-chords.com/findnotes ... 4=&n5=&n6=

I don't know, just a shot in the dark. You could call it Dave.
Jan could tell you.

[Hink]

F6/A 1=F
Bm7b9/A 1=B 5=F#
Bbmaj9/A 1=Bb 5=F

[jancivil]

There's no way to call it. If we're looking for chords built by thirds, there is one third in that, A to C.

[Functional]

Am with an eleventh, simple as that really. It could be something else depending on context, but just these three notes with no additional context would suggest that it's a simple A minor chord. The eleventh there doesn't really change anything, but if you really need a name for it then Am(add11).

[Farnaby]

simple as that really.

Not simple really, we already have a few choices to consider.
Without context it doesn't really matter anyway. A collection of notes can be interpreted in many different ways. As jancivil has said - you can't call it.
Personally I see the A and C as appogiaturas descending to a major triad on G.
Clearly, and any true musician would agree with me, this is a G major chord.

[jancivil]

it's not as simple as all that, it may well <probably be Am (add11)> if we're naming chords strictly by thirds; but we have literally no context, no *music* in which to place it. We can't really know it's not eg., some chord of the seventh from D.

We may think 'probably not' to harmonies stemming from B or Bb with no such notes in evidence, but lacking context utterly we don't even have that.

[Functional]

If they say "A aeolian mode", as meaningless as it is otherwise, it does suggest that it's probably something about tonic harmony and A-C-D, with or without the E, is rather common there . I agree that without context it could be anything, but doesn't mean that there isn't a probable answer anyway, just like someone asking what is A-C-E

[jancivil]

I'll buy the probably, Occam's Razor rules ok, if we have to guess ("probably" is not really an *answer*).
I couldn't call it a chord yet, for that matter, I have no sense of where it's coming from (or what position or voicing); and frankly I'd take "A Aeolian" with a grain of salt at this juncture.

if it's middle C, a D a tone above and the A above that on a guitar I'm fairly inclined towards a chord of the seventh on D: F C D A which needs really no more suppositions than Am (add11) and as a practical matter has more sense to it IME.
The notes in that position do not strike me as particularly common chording as it stands; with an F below it is.

as to assuming the naivety has produced definitely an A root from the words A Aeolian, I don't

[Functional]

as to assuming the naivety has produced definitely an A root from the words A Aeolian, I don't

What I mean is that they probably limited themselves to using that particular scale. Why that might be relevant, I'll get back to it later.

I think it's safe to assume that the notes appear vertically in the order OP put them. There's a chance they don't (just like there's a chance they mispelled a note) - but people tend to do that intuitively from my experiences, including beginners.

And if we consider this configuration itself, the ACD. Is it common on its own? I dunno, it's probably not super common as you said. But if you play it tightly voiced, or give a major ninth worth of space between C-D, the sonority of Am is pretty dead easy to establish.

Which brings us to how one can easily get something like that. Since melodically speaking, in the key of A minor, D is probably the the least directional tone after E assuming you don't play V-chords (and some call that type of V-less harmony as "aeolian"; I'm inclined to call it just embellishments of tonic region).

Case in point, this. Pretty beginner-friendly stuff and you can just keep hammering that D. Eventually I bring in the E as well mostly because I kept hearing pedaling that alongside as a missed opportunity. I might be wrong on this, but I do feel that this kind of stuff is more common these days. There's even more you could do but it all sounds "the same" to me. Like i-v-bVI-bVI or i-v-IV-IV, i-bVII-IV-IV. It's all the same stuff that goes nowhere and you can mostly just use that D mindlessly in that context.

[Vurniks]

Try https://www.music-chords.com/exercises/chords-analyzer

The free online tools says there are 15 possible meanings of this chord.

[jancivil]

The words A/root note probably indicates A at the bottom of the chord. I mean I don't make assumptions 'this is definitely _', and given the paucity of other information...

"The free online tools says there are 15 possible meanings of this chord."
IE: you have nothing, and ignore that people are contributing actual ideas in their own words.
The literal answer is 'this is not a chord'. So the tool or tools is/are not credible for a real answer any more than people here, and certainly should not be expected to replace one's own enquiry into the matter.

I'm actually quite exceeding the question from the outset, as an exercise, and for the rest of readers; to be more food for thought. The OP (no response from the person in 4 days) isn't enough to remain the point of the thread IME.

"If it's <chord by thirds> we have one, A to C" looks a sufficient response to the original post. Am and an 11 is present, as far as that goes.

[TribeOfHǫfuð]

'this is not a chord'.

Agree, it is just a brief movement of voices. Everyone should be able to see where it ends: D is on its way to E, and we got a complete Am triad. Piece O cake. What do people need all these cryptic chord symbols for?

https://www.youtube.com/watch?v=5NPBIwQyPWE

I can see Peter's baffled face compared to just handing him the note sheet.

[jancivil]

Well, for that matter A C D is a nice kind of open sonority. As a sonority I very much like A C D G. (Maybe at this point, 4 notes, hey, we can call chords. Am11 is perfectly cromulent now.)

At this point we get into interest, and exceeding the restrictions of yer Theory 101. I don't want to make a chord name for A C D, for the beginner. I think the OP may have abandoned, tho. We can look at the object and investigate possibilities.

So, voice-leading, part-writing. Does the D have to go to E to satisfy the most obvious rudimentary kind of chord block? What's the idea? One hasn't been mentioned in the original post.
It can stay D and the C to B - A B D, is there a law against either? - and the A to G... or just float pandiatonically.
Since we're more or less in agreement it's a partial chord thingy, why can't that be part of E A D G C.
I see that aggregate, with a maj.2, and freely think other things. C G D A E, both of these voiced however. C D E F G A.
C D G is Zappa's "2 chord", a whole practice of chords that don't have thirds, unburdened by major/minor quality concerns. I don't have to think of the OP as a naif that has to be led into the light of (or have their mind closed to) triads-all-day-long.

As an abstraction, not quite a chord; it's not music yet and music doesn't have to be this all chords notion, we aren't forced to require an object to be an A minor chord. A person new to music doesn't have to be managed like that, do they.

[TribeOfHǫfuð]

Well, I better like this ^ kind of speculation compared to chord naming if we are to speculate. Tho, we obviously have to make up a musical context for the OP to make it sensible to even try.