Regular join should include one? (7)
I believe the answer is:
soldier
'regular' is the definition.
(regular can mean a regular soldier)
'join should include one?' is the wordplay.
I cannot really understand how this works, but
'one?' could be 'i' (roman numeral) and 'i' is located in the answer.
'join' could be 'solder' (soldering is a kind of joining) and 'solder' is located in the remaining letters.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for soldier that I've seen before include "Army fighter" , "Server in army" , "Strip of toast to go with a boiled egg" , "Member of a fighting force" , "Military person" .)