Partial to one, as in bed (6)
I believe the answer is:
biased
'partial' is the definition.
(similar in meaning)
'one as in bed' is the wordplay.
'one' becomes 'i' (Roman numeral).
'in' indicates putting letters inside.
'i'+'as'='ias'
'ias' put within 'bed' is 'BIASED'.
'to' acts as a link.
(Other definitions for biased that I've seen before include "Prejudiced or partisan" , "'One-sided, slanted (6)'" , "Prejudiced or influenced in favour or against" , "Having favourite" , "Influenced unfairly" .)