Offer to be a watchman (6)
I believe the answer is:
tender
'offer' is the definition.
(tender can mean to offer something)
'be a watchman' is the wordplay.
'be' becomes 'tend' (tending is a kind of being).
'a watchman' becomes 'er' (I can't justify this - if you can you should believe this answer much more).
'tend'+'er'='TENDER'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for tender that I've seen before include "Offer; delicate" , "Delicate or kindhearted" , "Caring" , "Ship's boat" , "One who cares" .)