One who has been ''disarmed''? (7)
I believe the answer is:
amputee
'one who has been ''disarmed''?' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
This is all the clue.
(Other definitions for amputee that I've seen before include "Person with limb(s) removed" , "man with frostbitten toes, once?" , "Person with a limb severed" , "One who's had a limb removed in surgery" , "Someone who has had a limb surgically removed" .)