single entry vs single-entry bookkeeping

single entry and single-entry bookkeeping both are nouns.

Word	Noun	Adjective	Verb	Adverb
single entry	Yes	No	No	No
single-entry bookkeeping	Yes	No	No	No

As nouns, single entry and single-entry bookkeeping are synonyms defined as:

single entry and single-entry bookkeeping: a simple bookkeeping system; transactions are entered in only one account

single entry (noun)	single-entry bookkeeping (noun)
a simple bookkeeping system; transactions are entered in only one account	a simple bookkeeping system; transactions are entered in only one account