Giant can, accepting thanks (5)
I believe the answer is:
titan
'giant' is the definition.
(I know that giant can be written as titan)
'can accepting thanks' is the wordplay.
'can' becomes 'tin' (both are metal containers).
'accepting' indicates putting letters inside (inserted letters are accepted).
'thanks' becomes 'ta' (UK informal version of 'thank you').
'tin' enclosing 'ta' is 'TITAN'.
(Other definitions for titan that I've seen before include "A son of Uranus and Gaea" , "Mythological giant" , "Atlas, possibly" , "Colossus" , "Saturn's moon" .)