Credit us with a fast finish, though it's hard (5)
I believe the answer is:
crust
'it's hard' is the definition.
I can't judge whether this defines the answer.
'credit us with a fast finish' is the wordplay.
'credit' becomes 'cr' (abbreviation).
'with' says to put letters next to each other.
'finish' suggests the final letters.
The final letter of 'fast' is 't'.
'cr'+'us'+'t'='CRUST'
'though' is the link.
Can you help me to learn more?
(Other definitions for crust that I've seen before include "Pie topping" , "Bit of toast, perhaps" , "Tough part of twenty two down" , "Hardened layer; pie top" , "Hard knowledge" .)