Blonde can be reasonable (4)
I believe the answer is:
fair
I believe this clue is a double definition.
'blonde' is the first definition.
(similar in meaning)
'reasonable' is the second definition.
(I know that reasonable can be written as fair)
'can be' is the link.
(Other definitions for fair that I've seen before include "kind of entertainment" , "Just; passable" , "Equitable, just (4)" , "Just right" , "Decent" .)