Believe, after a century, one can get tired! (6)
I believe the answer is:
credit
'believe' is the definition.
(I know that believe is a kind of credit)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for credit that I've seen before include "Direct (anag) - tick" , "Belief - trust - favourable acknowledgment" , "entry in cashbook" , "(Account) sum received" , "'Give ...... where ...... is due'" .)