(n.) an olive harvest
An oleity is an olive harvest.
That’s a word apparently coined by the English lexicographer Thomas Blount in his 1656 dictionary, Glossographia (and admittedly seldom used since).
Etymologically, it derives from the Latin word for an olive harvest, oleitas, which is itself rooted in the Latin word for an olive, olea. The –ity ending is the standard English interpretation of the Latin noun-forming suffix –itas; the same unit forms nouns like purity and superiority from their underlying roots.