Lab coat? (3)
I believe the answer is:
fur
'lab coat?' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for fur that I've seen before include "Coating formed on sick person's tongue (3)" , "Coating formed on tongue of sick person" , "Deposit inside kettles" , "Expensive coat; deposit in kettle" , "Deposit lining kettles" .)