Lament life's end, and the end of masterly, welcoming supporter (5)
I believe the answer is:
elegy
'lament' is the definition.
(I know that lament can be written as elegy)
'life's end and the end of masterly welcoming supporter' is the wordplay.
'end' suggests the final letters.
'and' means one lot of letters go next to another.
'the end of' says to take the final letters.
'welcoming' means one lot of letters goes inside another (in sense of 'inviting in').
'supporter' becomes 'leg' (I've seen this in another clue).
The last letter of 'life' is 'e'.
The last letter of 'masterly' is 'y'.
'e'+'y'='ey'
'ey' placed around 'leg' is 'ELEGY'.
(Other definitions for elegy that I've seen before include "Milton's Lycidas?" , "A sorrowful poem - Gray wrote a famous one" , "Plaintive poem" , "Poetic lament for the dead" , "Lines written by poet" .)