One recommending plug protection (7)
I believe the answer is:
advisor
'one recommending' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'plug protection' is the wordplay.
'plug' becomes 'ad' (as in plugging a product).
'protection' becomes 'visor' (visor is a kind of protection).
'ad'+'visor'='ADVISOR'
Can you help me to learn more?
(Other definitions for advisor that I've seen before include "Mentor, counsel" , "consultant" , "Guide; VI roads (anag.)" , "I recommend" , "One recommends" .)