One who calls five, is it? Or all combined? (7)
I believe the answer is:
visitor
'one who calls' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'five is it? or all combined?' is the wordplay.
I cannot really see how this works, but
'five' could be 'v' (Roman numeral) and 'v' is found in the answer.
'is' is found in the answer.
'it?' could be 't' (abbreviation. e.g. in 'tis) and 't' is found within the answer.
'or' is within the answer.
A single letter 'i' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for visitor that I've seen before include "She calls" , "Guest - tourist" , "One coming to call" , "Person turning up" , "Someone calling (again at 23?)" .)