Student with strange belief opening the preserver (4,4)
I believe the answer is:
life belt
'preserver' is the definition.
(I know that life belt is a type of preserver)
'student with strange belief opening the' is the wordplay.
'student' becomes 'l' (as in L-plates for learner drivers).
'with' is a charade indicator (letters next to each other).
'strange' indicates anagramming the letters.
'opening' suggests taking the first letters.
The initial letter of 'the' is 't'.
'belief' anagrammed gives 'ifebel'.
'l'+'ifebel'+'t'='LIFE BELT'
(Other definitions for life belt that I've seen before include "Aid to survival at sea" , "Buoyant ring to aid person in danger of drowning" , "It is thrown to swimmer in difficulties" , "Sailor's safety ring" , "Drowning preventer" .)