za ¦ the second of the three sibilants (it belongs to the cerebral class, and is sometimes substituted for s, and more rarely for S, and occasionally interchangeable with K; in sound it corresponds to sh in the English word shun; many roots which begin with s are written in the Dhātu-pāṭha with z, prob. to show that their initial s is liable to be cerebralized after certain prepositions).
Sanskrit Dictionary