Apart from a second subordinate (7)
I believe the answer is:
asunder
'apart from' is the definition.
(thesaurus)
'a second subordinate' is the wordplay.
'second' becomes 's' (common abbreviation).
'subordinate' becomes 'under' (similar in meaning).
'a'+'s'+'under'='ASUNDER'
(Other definitions for asunder that I've seen before include "Apart - in pieces" , "Sad rune (anag.)" , "(Rent) apart" , "(Torn) into parts" , "Apart (archaic)" .)