Overburdened with a word (4)
I believe the answer is:
verb
'a word' is the definition.
(verb is a kind of word)
'overburdened with' is the wordplay.
'with' indicates the answer is hidden within the clue.
'VERB' is hidden within 'overburdened'.
(Other definitions for verb that I've seen before include "Old-fashioned art, for example" , "'In grammar, it denotes action (4)'" , "Type of word indicating action" , "Maybe protest" , "Word that denotes an action or a state" .)