An item that is especially noteworthy for its value, rarity, and/or history and would thus be prized by someone who collects such things. We went through my grandfather's attic and came upon a number of different collector's items, from rare toys to vintage rifles.
An object of great interest, value, or rarity, as in This necklace is a collector's item. Originating in the early 1900s as collector's piece, a usage still common in Britain, the term in its present form is occasionally transferred to persons as well, as in The Beach Boys became a collector's item on the tour. [c. 1930]