Wit's formula, so sad, spouted with one passing away? (6,4,5)
I believe the answer is:
famous last words
'passing away?' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.
'wit's formula so sad spouted with one' is the wordplay.
I cannot really see how this works, but
'so' could be 'as' (eg 'not as tall as me' means 'not so tall as me') and 'as' is found in the answer.
'with' could be 'w' (abbreviation) and 'w' is located in the answer.
'one' could be 'a' (a thing is one thing) and 'a' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for famous last words that I've seen before include "Ill-judged comment" , "Passing comment" .)