Copper, say, encountered a student (5)
I believe the answer is:
metal
'copper say' is the definition.
(I know that copper 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 "Maybe copper" , "Conducting solid" , "Eg, copper" , "Maybe lead" , "Tungsten, for example" .)