Way to evaluate chair (8)
I believe the answer is:
moderate
'chair' is the definition.
(I know that chair can be written as moderate)
'way to evaluate' is the wordplay.
'way' becomes 'mode' (synonyms).
'to evaluate' becomes 'rate' (rating is a kind of evaluating).
'mode'+'rate'='MODERATE'
(Other definitions for moderate that I've seen before include "Dare me to (anag) - act as an arbitrator" , "Slacken" , "Make less severe" , "So-so; sensible" , "Not extreme - not very good" .)