Student teacher one chewing cud (5)
I believe the answer is:
llama
'one chewing cud' is the definition.
(animal which chews cud)
'student teacher' is the wordplay.
'student' becomes 'L' (learner, as in L-plates for learner drivers).
'teacher' becomes 'lama' (a lama is a spiritual teacher in Buddhism).
'l'+'lama'='LLAMA'
(Other definitions for llama that I've seen before include "Wool producer" , "South American native" , "woolly customer" , "South American cud-chewing mammal" , "Andean 'camel'" .)