Many a uniform's a bad fit, so let's have civvies! (5)
I believe the answer is:
mufti
'civvies' is the definition.
(both can mean non-uniform)
'many a uniform's a bad fit' is the wordplay.
'many' becomes 'm' (Roman numeral for a thousand).
'a uniform' becomes 'U' (phonetic alphabet: alpha, bravo, charlie etc.).
'a bad' indicates an anagram.
'fit' is an anagram of 'fti'.
'm'+'u'+'fti'='MUFTI'
'so let's have' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for mufti that I've seen before include "Civilian dress (for serviceman)" , "Plain clothes - Muslim law expert" , "Civilian clothes worn by service personnel" , "Civilian attire" , "Civilian gear" .)