Fail to correspond (6)
I believe the answer is:
differ
This clue might be a double definition.
'fail' is the first definition.
Although both the answer and definition are verbs in their base form, I don't understand how one could define the other.
'correspond' is the second definition.
The definition and answer can be both to do with communicating as well as being verbs in their base form.
Perhaps you can see an association between them that I can't see?
'to' is the link.
Can you help me to learn more?
(Other definitions for differ that I've seen before include "Disagree (with someone)" , "Disagree, take issue" , "Be of opposing opinion" , "Contrast - disagree" , "Disagree or vary" .)