Always, poetically (3)
I believe the answer is:
'always poetically' is the definition.
('e'er' is an archaic version of 'ever')
This is the entire clue.
(Other definitions for eer that I've seen before include "Before, poetically speaking (1'2)" , "Ever to the poet (3)." , "Ever poetically" , "Always (poetical)" , "Always (poetic)" .)