YISHAR KOḤEKA ("May thy strength be firm"):
A frequent exclamation and expression of thanks. The first part of the formula is derived by Levy and Kohut from "yashar" = "to be firm or healthy." The phrase occurs in the Talmud in the Hebrew form "yishar koḥeka" (Shab. 87a) and in the Aramaic form "yishar ḥeylak" (Shab. 53a, 62b; Lam. R. 52b; Gen. R. 54), and is now used, for example, as a response to the preacher after the sermon, to the ḥazzan after the prayer, and to the priest after the priestly blessing, while it serves as a formula of thanks also.
