Copper maybe encountered a student (5)
I believe the answer is:
metal
'copper maybe' is the definition.
(I know that Cu is a type of metal)
'encountered a student' is the wordplay.
'encountered' becomes 'met' ('meet' can be a synonym of 'encounter').
'student' becomes 'l' (as in L-plates for learner drivers).
'met'+'a'+'l'='METAL'
(Other definitions for metal that I've seen before include "Given lead, perhaps" , "Conducting solid" , "barium?" , "Element eg for road or rail" , "tin, perhaps" .)