Seek interminably to understand (3)
I believe the answer is:
see
'understand' is the definition.
(synonyms)
'seek interminably' is the wordplay.
'interminably' means to remove the last letter.
'seek' with its final letter taken away is 'SEE'.
'to' is the link.
(Other definitions for see that I've seen before include "around cathedral" , "Observe the bishop's domain" , "date" , "Norwich, for example" , "Perceive a bishopric" .)