2. An object used to make a determination or choice at random: "casting lots."
3. The use of objects in making a determination or choice at random: "chosen by lot."
4. Something that befalls one because of or as if because of determination by lot.
5. Etymology: from Old English hlot, "object (anything from dice to straw, but often a chip of wood with a name inscribed on it) used to determine someone's share"; also, "what falls to a person by lot".
An object was placed with others in a receptacle, which was shaken, the winner being the one that fell out first; hence, to cast lots. In some cases the lots were drawn by hand.
The sense of "plot of land" is first recorded in 1633 (distribution of the best property in new settlements often determined by casting lot), that of "group, collection" is 1725, from the notion of auction lots.
The generalized sense of "many" is first attested in 1812. To cast (one's) lot with another is to agree to share the winnings of something.