item vs agenda item

item and agenda item both are nouns.

Word	Noun	Adjective	Verb	Adverb
item	Yes	No	No	Yes
agenda item	Yes	No	No	No

As nouns, agenda item is a hyponym of item; that is, agenda item is a word with a more specific, narrower meaning than item:

item: a distinct part that can be specified separately in a group of things that could be enumerated on a list
agenda item: one of the items to be considered

Other hyponyms of item include incidental, inventory item, line item, news item, place, position.

item (noun)	agenda item (noun)
a whole individual unit; especially when included in a list or collection	one of the items to be considered
an isolated fact that is considered separately from the whole
a distinct part that can be specified separately in a group of things that could be enumerated on a list
an individual instance of a type of symbol
a small part that can be considered separately from the whole

item (adverb)	agenda item (adverb)
(used when listing or enumerating items) also