Employment on Sunday in plant (5)
I believe the answer is:
works
'plant' is the definition.
(I know that plant can be written as works)
'employment on sunday' is the wordplay.
'employment' becomes 'work' (synonyms).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'sunday' becomes 's'.
'work'+'s'='WORKS'
'in' is the link.
(Other definitions for works that I've seen before include "Employs physical or mental effort" , "Functions" , "Plants; operates" , "Factory; has a job" , "Acts: the > opera" .)