One was aware king's departed again (4)
I believe the answer is:
anew
'again' is the definition.
(synonyms)
'one was aware king's departed' is the wordplay.
'one' becomes 'a' (a thing is one thing).
'was aware' becomes 'knew' (I've seen this before).
'king' becomes 'K' (chess abbreviation).
'departed' indicates named letters should be taken away.
'knew' with 'k' removed is 'new'.
'a'+'new'='ANEW'
(Other definitions for anew that I've seen before include "From the beginning again" , "Once more (poetic)" , "Afresh" , "Again but differently" , "Wane in a different way, again" .)