What is the X in X-mas?
1590s, "pass off in the form of a vapor or liquid," from Middle French transpirer (mid-16c.), from Latin trans- "through" (see trans-) + spirare "to breathe" (see spirit). Figurative sense of "leak out, become known" is recorded from 1741, and the erroneous meaning "take place, happen" is almost as old, being first recorded 1755. Related: Transpired; transpiring.