Juliet needs a minder, mostly for cat (6)
I believe the answer is:
jaguar
'for cat' is the definition.
(jaguar is a kind of cat)
'juliet needs a minder mostly' is the wordplay.
'juliet' becomes 'J' (phonetic alphabet: alpha, bravo, charlie etc.).
'needs' is a charade indicator (letters next to each other).
'minder' becomes 'guard' (minder can mean a bodyguard).
'mostly' means to remove the last letter (most but not all of the word).
'guard' with its final letter removed is 'guar'.
'j'+'a'+'guar'='JAGUAR'
(Other definitions for jaguar that I've seen before include "Large jungle cat" , "Large black-spotted cat" , "Hands on hips, elbows projecting" , "Big cat of tropical America" , "Wildcat" .)