two-a-penny vs twopenny-halfpenny

two-a-penny and twopenny-halfpenny both are adjectives.

Word	Noun	Adjective	Verb	Adverb
two-a-penny	No	Yes	No	No
twopenny-halfpenny	No	Yes	No	No

As adjectives, two-a-penny and twopenny-halfpenny are synonyms defined as:

Other synonyms of two-a-penny include sixpenny, threepenny, tuppeny, twopenny.

two-a-penny (adjective)	twopenny-halfpenny (adjective)
of trifling worth	of trifling worth