Lachesis was one of the Fates, and her name literally means 'drawing of lots' (lachesis) from lanchano, 'to obtain by lot', 'draw lots'. She was thus the goddess who 'apportioned' a person's life, who laid down (or measured) what one's lot in life should be.
Compare the names of the other Fates - Clotho and Atropos. Clotho, whose name suggests spinning, came to give the three a consecutive ordering of a person's destiny, with Clotho drawing the thread of life out, Lachesis measuring it, and Atropos cutting it of.