A weathercock is a metal arrow or pointer that sits on top of a roof, church tower or barn and turns to show which way the wind is blowing. It is a weather vane, and "weathercock" is the name for one shaped like a rooster — a male chicken standing with its tail up, the shape you see on old European churches. Because that shape was so common for so long, the two words became almost interchangeable in ordinary speech. Why a rooster? The tradition is European and church-linked, and people have told various stories about it over the centuries; I would not swear to any single explanation. What is certain is that by the Middle Ages the cockerel on the spire was ordinary enough for English to have this compound word for it. Today the word feels old and rural. You meet it in stories, poems, tourist descriptions of old villages, and crossword puzzles far more than in conversation — most modern speakers just say "weather vane". It also has a figurative use worth knowing. Call a person a weathercock and you mean they change their opinion whenever the mood around them changes — they always point wherever the wind is blowing. It is a criticism, usually about politicians, and it is more common in British English and in older writing. The picture is lovely and easy to remember: the thing on the roof has no opinion of its own; it only shows what the air is doing.

風信雞（屋頂上公雞造型的風向標；就是 weather vane 的一種）。比喻人時＝牆頭草、風向球，指立場隨風轉的人。這個字偏舊、偏文學，現在一般說 weather vane