(Caveat: this may be more appropriate in the English Stack Exchange, but I’m a musician and it has to do with instruments, so I put it here.)
As a composer of Celtic-style tunes, I usually pick up my mandolin and noodle in a few keys that work well on a mando, like G, D, Am, Bm for example. I almost never play in Eb (=Cm), say, because without resorting to fully-fretted positions it’s not “natural” for a mandolin. The word “affordance,” as used in a user-interface way, has some bearing here: the way a mandolin is physically organized “affords” ease of use in some keys over others. (The affordance of a door handle is obvious: it says “pull me.” A flat plate on a door says “push.”)
Now on a piano the layout, and how I play the instrument, is different from a mandolin. Whereas the mando is organized across four courses of strings arranged in fifths, and the hands have different jobs (picking and fretting), the piano is laid out in a linear array and both hands play notes. The “affordance” is different. It’s much easier to play in Cm (and for me, D on a piano is sort of hard). If I compose a piece on piano and try to play it on mando, I am struck by how I would never have thought of it on a mando.
Pick your instrument - a penny whistle is key-oriented and range-limited, so only certain types of tune easily fall under the fingers. Drums are a whole different kettle (no pun) of fish: you use sticks and much of your body to play.
So here is the question: what word you would use to describe the instrument’s native character? I have used “affordability” here but that only refers to a part of the approach to the instrument. For some reason the word “modality” comes to mind (not in the scales/modes sense) but I have not been able to support that guess.
The word would be used like this: “ Composing Irish tunes on a fiddle is easier than on a harmonium because the [?word?] of the instrument is more appropriate. Almost-candidates include words like: “feel,” “character,” “voice,” “style,” or “capability.”
This question is not just about finding the word. I think the whole concept of different instruments leading to different compositions is intriguing. Comments?