lightening

Etymology 1
.

Noun

 * 1) The act or result of making something light or lighter.
 * 2)  The sensation caused by the descent of the uterus into the pelvic cavity before the onset of labour
 * 3)  The removal of cargo (especially crude oil) from a vessel in order to reduce its draft
 * 1)  The removal of cargo (especially crude oil) from a vessel in order to reduce its draft

Usage notes
Regarded as a misspelling by all modern authorities.