He's coming down - for the day! (7)
I believe the answer is:
tripper
'he's coming down for the day' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he's' is the wordplay.
I cannot really see how this works, but
'he' could be 'tripp' and 'tripp' is present in the answer.
The remaining letters 'er' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for tripper that I've seen before include "One who makes an excursion" , "Tourist" , "One hoping to enjoy journey" , "person having highly enjoyable experience?" , "at risk of sustaining injury?" .)