In IIMC, a lecturer turned hostile (8)
I believe the answer is:
'hostile' is the definition.
(similar in meaning)
'in iimc a lecturer turned' is the wordplay.
'lecturer' becomes 'l'.
'turned' indicates anagramming the letters.
'iimcal' anagrammed gives 'imical'.
(Other definitions for inimical that I've seen before include "Injurious - hostile" , "In claim I am strangely hostile" , "Hostile or in opposition" , "Hostile, unfavourable" , "Unfriendly or unfavourable" .)