Hostile lecturer blocks one student
I believe the answer is:
ill
'hostile' is the definition.
(similar in meaning)
'lecturer blocks one student' is the wordplay.
'lecturer' becomes 'l' (abbreviation for lecturer).
'blocks' indicates putting letters inside (the inside letters form a 'blockage').
'one' becomes 'i' (Roman numeral).
'student' becomes 'l' (as in L-plates for learner drivers).
'i'+'l'='il'
'l' placed inside 'il' is 'ILL'.
(Other definitions for ill that I've seen before include "state of America" , "Badly diminished" , "Sickly" , "Badly - in need of treatment" , "Ailing" .)