A hat? Let it stay, boy (7)
I believe the answer is:
stetson
'a hat?' is the definition.
(I know that Stetson is a type of hat)
'let it stay boy' is the wordplay.
'let it stay' becomes 'stet' (I've seen this in another clue).
'boy' becomes 'son' (synonyms).
'stet'+'son'='STETSON'
(Other definitions for stetson that I've seen before include "Hat for country-and-western singers, Texan oil magnates, etc." , "Large hat" , "Ten-gallon hat" , "Cowboy wear" , "Tip" .)