Companion equal to rent review (7)
I believe the answer is:
partner
'companion' is the definition.
(I've seen this before)
'equal to rent review' is the wordplay.
'equal' becomes 'par'.
'to' says to put letters next to each other.
'review' says the letters should be written backwards.
'rent' reversed gives 'tner'.
'par'+'tner'='PARTNER'
(Other definitions for partner that I've seen before include "sometimes joining in crime" , "A person dancing with another" , "teammate" , "Other half?" , "Comrade" .)