Cast worth altering (5)
I believe the answer is:
throw
'cast' is the definition.
(synonyms)
'worth altering' is the wordplay.
'altering' indicates an anagram.
'worth' with letters rearranged gives 'THROW'.
(Other definitions for throw that I've seen before include "Toss" , "puzzle" , "A turn with the dice" , "Try to lose" , "Propel through the air" .)