† ChelidonyObs. Forms: 6 chalydony, 7 chelydoin. [ad. L. chīlidonius (lapis), F. chelidoine.] The same as celidony2. 1586Bright Melanch. xxxix. 257 The chalydony, or swallowe stone, found in the mawes of young swallowes.1622Peacham Compl. Gentl. (1661) 171 Diamond, Agate, or Chelydoin.