Go for a frock and hat? (9)
I believe the answer is:
headdress
'hat?' is the definition.
(hat is a kind of headdress)
'go for a frock' is the wordplay.
'go' becomes 'head' (I've seen this in another clue).
'for' says to put letters next to each other.
'a frock' becomes 'dress' ('dress' can be a synonym of 'frock').
'head'+'dress'='HEADDRESS'
'and' is the link.
(Other definitions for headdress that I've seen before include "capital investment" , "Top cover" , "Plumed helmet" , "Ceremonial wear" , "Hat or tiara, say" .)