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lightning vs. lightening

lightning

[lahyt-ning] / ˈlaɪt nɪŋ /

noun

a brilliant electric spark discharge in the atmosphere, occurring within a thundercloud, between clouds, or between a cloud and the ground.

verb (used without object)

lightninged, lightning

to emit a flash or flashes of lightning (often used impersonally with it as subject).

If it starts to lightning, we'd better go inside.

adjective

of, relating to, or resembling lightning, especially in regard to speed of movement: lightning speed.

lightning flashes;
lightning speed.

idioms

catch lightning in a bottle. catch lightning in a bottle.

lightening

[lahyt-n-ing] / ˈlaɪt n ɪŋ /

noun

Medicine/Medical.

the descent of the uterus into the pelvic cavity, occurring toward the end of pregnancy, changing the contour of the abdomen and facilitating breathing by lessening pressure under the diaphragm.