Amuses wildly, let's say (6)
I believe the answer is:
assume
'let's say' is the definition.
'assume' can be an answer for 'say' (thesaurus). I'm not certain of the 'let's' bit.
'amuses wildly' is the wordplay.
'wildly' indicates an anagram.
'amuses' is an anagram of 'ASSUME'.
Can you help me to learn more?
(Other definitions for assume that I've seen before include "Be arrogant" , "Take for granted or agreed" , "Claim without justification" , "Suppose; put on" , "Wrongly take" .)