Time chap switched firm (8)
I believe the answer is:
emphatic
'firm' is the definition.
(I've seen this in another clue)
'time chap switched' is the wordplay.
'switched' indicates anagramming the letters (letters switch places).
'time'+'chap'='timechap'
'timechap' anagrammed gives 'EMPHATIC'.
(Other definitions for emphatic that I've seen before include "Forceful and definite" , "Direct" , "Forceful - pronounced" , "Forceful in expression" , "Expressing oneself with vigour and conviction" .)