means To curve the corners of your mouth upward as an expression of pleasure, friendliness, or amusement.

from From Middle English smilen, which surfaced in English around the 13th century and likely arrived from a Scandinavian source — compare Swedish smila and Danish smile. It belongs to a wide Germanic family tied to a root meaning 'to laugh' or 'to be amazed,' and it's a distant cousin of the older English smerian (to laugh at) and even of Latin mirari, 'to wonder at' — the same root that gives us 'miracle' and 'admire.' Before 'smile' settled in, English mostly used 'smirk,' which once simply meant to smile and only later soured into something sly.