In the course of, in the time of, throughout the continuance of.
M.E. Duryng, durand, pr.p. of duren "to last, endure, continue, be or exist," from O.Fr. durer, from L. durare "to harden," from durus "hard;" PIE root *deru- "be firm, solid, steadfast."
Tarpây, literally "lasting over time," from tar- "through, across, over time," variant tarâ-, → trans-, + pây present stem and agent noun of pâyidan, → last (v.).