LIGHTNING: The occurrence of a natural electrical discharge of very short duration and high voltage between a cloud and the ground or within a cloud, accompanied by a bright flash and typically also thunder.
LIGHTENING: A drop in the level of the uterus during the last weeks of pregnancy as the head of the fetus engages in the pelvis.
Please stop mixing these two up. I keep picturing giant babies emerging from the storm clouds whenever someone spells lighting with an ‘e’.