167. In a few very rare cases

In a few very rare cases, final radical s before s is changed to t (perhaps by dissimilation): they are, from √vas dwell (also sporadically from vas shine, ÇB., and vasclothe, Har.), the future vatsyā́mi and aorist ávātsam; from √ghas, the desiderative stem jíghatsa.

a. For t as apparent ending of the 3d sing. in s-verbs, see 555 a.