Maid watchful when old bachelor goes missing (7)
I believe the answer is:
servant
'maid' is the definition.
(thesaurus)
I don't understand the remainder of the clue.
(Other definitions for servant that I've seen before include "Maid or butler, say" , "eg Sancho Panza" , "Perhaps help" , "Valet, e.g." , "Domestic attendant" .)