पृ

Etymology 1
Likely a specialized usage of पृ in the "fill up" or "further" senses described under Etymologies 2 and 3.

Root

 * 1) to be busy or active.
 * 2) to cause to work, engage upon, entrust with, appoint to (usually with locative case)
 * 3) to place, set, fix, direct, cast

Etymology 2
From.

Root

 * 1) to bring over or to (acc.), bring out of, deliver from (abl.), rescue, save, protect, escort, further, promote
 * 2) to surpass, excel (acc.)
 * 3) to be able (with inf.)