Collar said to be unfinished (5)
I believe the answer is:
rough
'be unfinished' is the definition.
(associated in meaning)
'collar said' is the wordplay.
'collar' becomes 'ruff' (ruff is a kind of collar).
'said' indicates a 'sounds like' (homophone) clue.
'ruff' sounds like 'ROUGH'.
'to' is the link.
(Other definitions for rough that I've seen before include "Boisterous - thug" , "Sketchy" , "Violent type" , "Not level or smooth, like part of golf course" , "Uneven, harsh" .)