Opening for French teacher on way back with relative — a thrill (7)
I believe the answer is:
frisson
'a thrill' is the definition.
('frisson' can be a synonym of 'thrill')
'opening for french teacher on way back with relative' is the wordplay.
'opening for' indicates taking the first letters.
'teacher' becomes 'sir' (I've seen this before**).
'on way back' says the letters should be written in reverse.
'with' is a charade indicator (letters next to each other).
'relative' becomes 'son' (son is a kind of relative).
The initial letter of 'french' is 'f'.
'sir' reversed gives 'ris'.
'f'+'ris'+'son'='FRISSON'
(Other definitions for frisson that I've seen before include "A shudder or thrill" , "Strong feeling of excitement, thrill" , "Kick" , "Emotional thrill" , "Shiver of excitement" .)