Moving aft? That's rich! (3)
I believe the answer is:
fat
'rich' is the definition.
(synonyms)
'moving aft?' is the wordplay.
'moving' indicates anagramming the letters.
'aft' is an anagram of 'FAT'.
'that's' is the link.
(Other definitions for fat that I've seen before include "Corpulent; little (chance)" , "eg Lard" , "Portly" , "Substantial" , "Overweight, stout" .)