Lightening vs Rightening - What's the difference?

As verbs the difference between lightening and rightening

is that lightening is present participle of lang=en while rightening is present participle of righten.

is the sensation caused by the descent of the uterus into the pelvic cavity before the onset of labour.

(head)

(en noun)

(medicine) The sensation caused by the descent of the uterus into the pelvic cavity before the onset of labour

(nautical) The removal of cargo (especially crude oil) from a vessel in order to reduce its draft

(head)