Make dim (5)
'make dim' is the definition.
(synonyms)
This is all the clue.
(Other definitions for blear that I've seen before include "Watery, blurred" , "Blur" , "Baler (anag.)" , "Indistinct" , "Make (the eyes) dim" .)
(Other definitions for darken that I've seen before include "Make less light" , "shade" , "Grow less light" , "Grow blacker" , "Dim" .)