Kha, cf. Greek , is generally “cavity”; and in the Ṛg Veda, particularly, “the hole in the nave of a wheel through which the axle runs” (Monier-Williams). In Journ. U.P. Hist. Soc., vii, 44–5 and 62, Mr. A. N. Singh shows conclusively that in Indian mathematiqal usage, current during the earlier centuries of the Christian era, kha means “zero”; Sūryadeva, commenting on Aryabhaṭa, says “the khas refer to voids (khāni śūnyā upa lakṣitdāi) … thus khadwnake means the eighteen places denoted by zeros”.