English member is first to thank one expressing mournful thoughts (7)
I believe the answer is:
elegist
'one expressing mournful thoughts' is the definition.
(someone writing an elegy)
'english member is first to thank' is the wordplay.
'english' becomes 'e' (abbreviation).
'member' becomes 'leg' (member can mean a limb).
'first to' suggests taking the first letters.
The initial letter of 'thank' is 't'.
'e'+'leg'+'is'+'t'='ELEGIST'
(Other definitions for elegist that I've seen before include "Composer of mournful songs" , "Writer of mournful verse" , "bemoaning linesman" , "Writer of reflective poems" , "Poet, e.g. Gray" .)