Courageous person detaining lecturer (4)
I believe the answer is:
bold
'courageous' is the definition.
('bold' is associated in meaning with 'courageous')
'person detaining lecturer' is the wordplay.
'person' becomes 'bod' (I've seen this in other clues**).
'detaining' means one lot of letters goes inside another.
'lecturer' becomes 'l'.
'bod' placed around 'l' is 'BOLD'.
(Other definitions for bold that I've seen before include "Audacious" , "Typeface with thick heavy lines" , "Daring, courageous" , "No chicken" , "Like heavy type" .)