Lachesis

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One of the three Fates, the measurer of the thread of destiny.

from The Century Dictionary.

• noun In classical mythology, that one of the three Fates whose duty it was to assign to each individual his destiny; the disposer of lots. She spun the thread or course of life from the distaff held by Clotho.
• noun In zoöl.:
• noun A genus of very venomous American serpents of the pit-viper or rattlesnake family (Crotalidæ), having a rudimentary rattle in the form of a spine. L. mutus is the deadly bushmaster of South America.
• noun Agenus of spiders nowcalled Laches.
• noun A genus of gastropods of the family Pleurotomidæ, of buccinoid figure with mammillated spire, as L. minima. Risso, 1826
• noun A genus of pseudoneuropterous insects of the family Psocidæ
• noun A genus of buprestid beetles, erected by Saunders in 1871 upon the African L. abyla, which had been placed in Œdisternon.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• proper noun Greek mythology One of the three Fates, or Moirae, daughter of Zeus and Themis; the measurer of the each thread of life.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the Greek goddess of fate who determines the length of the thread of life