Teacher has to care for a genius (10)
I believe the answer is:
mastermind
'a genius' is the definition.
(synonyms)
'teacher has to care' is the wordplay.
'teacher' becomes 'master' (I've seen this before).
'has' means one lot of letters go next to another.
'to care' becomes 'mind' (I've seen this in another clue).
'master'+'mind'='MASTERMIND'
'for' acts as a link.
(Other definitions for mastermind that I've seen before include "Ringleader" , "Brains" , "Knowledge-testing TV quiz" , "Brainy TV quiz" , "Person conceiving a project - TV programme" .)