Small instrument not in tune (5)
I believe the answer is:
sharp
'tune' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Maybe there's a link between them I don't understand?
'small instrument not' is the wordplay.
I cannot quite understand how this works, but
'small' could be 's' (abbreviation - e.g. clothes size) and 's' is found within the answer.
'instrument' could be 'harp' (harp is a kind of instrument) and 'harp' is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
'in' acts as a link.
Can you help me to learn more?
(Other definitions for sharp that I've seen before include "Punctually; raised note" , "Quick; pointed" , "Kind of musical note" , "Acidic; note" , "Acidic; smart and stylish" .)