For a time, the musical instrument is sharp (5)
I believe the answer is:
thorn
'sharp' 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?
'for a time the musical instrument' is the wordplay.
I cannot quite understand how this works, but
'time' could be 't' (abbreviation) and 't' is found in the answer.
'instrument' could be 'horn' (horn is a kind of instrument) and 'horn' is located in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'is' is the link.
Can you help me to learn more?
(Other definitions for thorn that I've seen before include "(Rose's) prickle" , "Sharp point; runic character" , "Sharp point on plant" , "pain in one's side" , "eg Prickle on rose" .)