Tusk takes four or forty. Finally! (5)
I believe the answer is:
ivory
'tusk' is the definition.
(synonyms)
'four or forty finally' is the wordplay.
'four' becomes 'IV' (roman numeral).
'finally' says to take the final letters.
The final letter of 'forty' is 'y'.
'iv'+'or'+'y'='IVORY'
'takes' is the link.
(Other definitions for ivory that I've seen before include "Substance of elephant's tusk" , "Material from elephant's tusks" , "Key perhaps" , "Some hunt this" , "recluse's tower?" .)