Pull horse over a crack (5)
I believe the answer is:
laugh
'crack' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Maybe you can see an association between them that I don't see?
'pull horse over a' is the wordplay.
'pull' becomes 'lug' (I've seen this before).
'horse' becomes 'h' (synonyms).
'over' is an insertion indicator.
'lug'+'h'='lugh'
'lugh' going around 'a' is 'LAUGH'.
Can you help me to learn more?
(Other definitions for laugh that I've seen before include "Show amusement or pleasure" , "Make sound expressing amusement" , "Chortle" , "Guffaw" , "Express joy or amusement" .)