Can't he keep a regular place? (5)
I believe the answer is:
nomad
'can't he keep a regular place?' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'can't he' is the wordplay.
'can't' becomes 'nom' (I can't explain this - if you can you should give a lot more credence to this answer).
'he' becomes 'Ad'.
'nom'+'ad'='NOMAD'
Can you help me to learn more?
(Other definitions for nomad that I've seen before include "Roving person" , "A wandering tribesman" , "Person of no fixed abode" , "Member of travelling people" , "Traveller with no permanent home" .)