Mean to say farewell with passion! (7)
I believe the answer is:
average
'mean' is the definition.
(I know that mean can be written as average)
'farewell with passion' is the wordplay.
'farewell' becomes 'ave' (Latin salutation).
'with' means one lot of letters go next to another.
'passion' becomes 'rage' (synonyms).
'ave'+'rage'='AVERAGE'
'to say' is the link.
(Other definitions for average that I've seen before include "It's common" , "Mean - medium" , "Medium; normal" , "Of no exceptional quality or ability" , "It may be mean" .)