means To lose your footing and slide unexpectedly, or more broadly to move, fall, or pass quietly and quickly from one place or state to another.

from From Middle English 'slippen,' likely borrowed from Middle Low German or Middle Dutch 'slippen,' meaning to slide or glide. It belongs to a slick Germanic family of words built on a root suggesting smooth, slimy, slippery things — a cousin of 'slime' and 'slick.' The sense of a small undergarment and a 'slip of paper' both grew from the same idea of something thin, narrow, and easily slid into place.