Unnecessary, one’s former nurse dipping into faulty Latin (12)
I believe the answer is:
nonessential
'unnecessary' is the definition.
(similar in meaning)
'one's former nurse dipping into faulty latin' is the wordplay.
'former nurse' becomes 'SEN' (state registered nurse - former UK nurse title).
'dipping into' is an insertion indicator.
'faulty' indicates anagramming the letters.
'ones'+'sen'='onessen'
'latin' with letters rearranged gives 'ntial'.
'onessen' put into 'ntial' is 'NONESSENTIAL'.
(Other definitions for nonessential that I've seen before include "Not absolutely necessary" , "Not required" , "Not totally necessary" , "Dispensable" .)