Swear to smuggle cat in border checkpoint (7)
I believe the answer is:
customs
'border checkpoint' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'swear to smuggle cat' is the wordplay.
'swear' becomes 'cuss' (synonyms).
'to smuggle' means one lot of letters goes inside another (smuggle can mean to secretly carry).
'cat' becomes 'tom' (a tom is a male cat).
'cuss' enclosing 'tom' is 'CUSTOMS'.
'in' is the link.
Can you help me to learn more?
(Other definitions for customs that I've seen before include "Traditions" , "Habits or import taxes" , "Import duties" , "Accepted practices" , "state's duties?" .)