single entry vs clerking

single entry and clerking both are nouns.

Word	Noun	Adjective	Verb	Adverb
single entry	Yes	No	No	No
clerking	Yes	No	No	No

As nouns, clerking is a hypernym of single entry; that is, clerking is a word with a broader meaning than single entry:

single entry: a simple bookkeeping system; transactions are entered in only one account
clerking: the activity of recording business transactions

Other hypernyms of single entry include bookkeeping.

single entry (noun)	clerking (noun)
a simple bookkeeping system; transactions are entered in only one account	the activity of recording business transactions