Nurse has a number, on the day (4)
I believe the answer is:
tend
'nurse' is the definition.
(tend can mean to nurse or look after)
'a number on the day' is the wordplay.
'a number' becomes 'n' (n can represent any number).
'on' indicates putting letters inside.
'the day' becomes 'ted' (I can't justify this - if you can you should believe this answer much more).
'n' placed into 'ted' is 'TEND'.
'has' acts as a link.
Can you help me to learn more?
(Other definitions for tend that I've seen before include "Minister" , "Wait on" , "Incline, lean" , "Be inclined to take care of" , "Care for, nurse" .)