For a smaller amount, the blockhead will give thanks! (5)
I believe the answer is:
bless
'give thanks' is the definition.
(thesaurus)
'for a smaller amount the blockhead will' is the wordplay.
I cannot really understand how this works, but
'smaller' could be 'less' (less great in size) and 'less' is found within the answer.
'amount' could be 'b' (B is an example) and 'b' is found within the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for bless that I've seen before include "Give honour to" , "Call God's favour upon" , "Praise - consecrate" , "perform consecration" , "Approve of" .)