Merges to highway with unknown directions (5)
I believe the answer is:
mixes
'merges' is the definition.
The answer and definition can be both related to change as well as being verbs in their -s form.
Maybe you can see an association between them that I don't see?
'highway with unknown directions' is the wordplay.
'highway' becomes 'mi'.
'with' says to put letters next to each other.
'unknown' becomes 'x' (algebra).
'directions' becomes 'es' (east and south - two directions).
'mi'+'x'+'es'='MIXES'
'to' is the link.
Can you help me to learn more?
(Another definition for mixes that I've seen is " Combines, blends".)