Who's last to be welcomed by assembled crewmen? (8)
I believe the answer is:
newcomer
'who's' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'last to be welcomed by assembled crewmen?' is the wordplay.
'last' says to take the final letters.
'be welcomed by' indicates putting letters inside (letters welcomed inside).
'assembled' is an anagram indicator.
The final letter of 'to' is 'o'.
'crewmen' with letters rearranged gives 'newcmer'.
'o' put within 'newcmer' is 'NEWCOMER'.
(Other definitions for newcomer that I've seen before include "2 arrival" , "He has just arrived or started" , "Late arrival" , "Fresh arrival" , "Novice" .)