An unknown person is comparatively odd (8)
I believe the answer is:
stranger
'an unknown person' is the definition.
(I've seen this before)
'comparatively odd' is the wordplay.
I cannot quite understand how this works, but
'odd' could be 'strange' (I've seen this before) and 'strange' is present in the answer.
A single letter 'r' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
'is' is the link.
Can you help me to learn more?
(Other definitions for stranger that I've seen before include "The unknown one is more unusual" , "More exotic" , "Newcomer, alien" , "Outsider" , "someone making nuisance call?" .)