MEANING: noun:
1. A device having a pointer rotating on a vertical spindle, used to indicate the direction of the wind.
2. Someone or something constantly changing.

ETYMOLOGY: From weather, from Old English weder + vane, from Old English fana (flag). Earliest documented use: 1721. Since a weather vane traditionally featured a rooster on top, it’s also known as a weathercock.

LEATHER VANE - a gadget made of tanned animal skin to tell the direction of the wind

EAT HER VANE - if you're really starving

WEATHER SANE - what we get less of as the earth's temperature rises