One way to hold this word: a big broad-winged bird turning slowly in wide circles, high up, beating its wings hardly at all. What is odd about buzzard is that the same name lands on two different birds on the two sides of the Atlantic - a hunter in Britain, a bird waiting for something already dead in America. The shape in the sky is what they share, and once the word moves to a person it is that same image of circling and waiting that comes with it.
Middle English bosart, from Anglo-Norman buisart and Old French busart, possibly from Latin buteo, a hawk. So the British hunting bird sits closest to the oldest meaning, and the word has no connection to buzz.
中古英文 bosart，來自古法文 busart，源頭可能是拉丁文 būteō（一種鷹）。所以英式那隻會獵食的鵟最接近它最早的意思；另外，這個字跟 buzz（嗡嗡聲）沒有關係。
packet evidence: Wiktionary etymology 1 for 'buzzard' (kaikki:3f6f69a190036ae4:225212204:46149)
From the picture
拿來說人
把鳥的印象搬到人身上：在旁邊繞著、等著佔便宜、不討人喜歡。北美口語的 old buzzard 就是這種味道，帶貶意，多半指脾氣壞或小氣的老人家。
noun · C2
In North American informal speech, an unpleasant person, especially an old man who is bad-tempered, mean or greedy. It nearly always appears as old buzzard.
老傢伙；壞脾氣的老頭
noun · B2
In British English, a large hunting bird with broad wings and a broad tail, which circles slowly high in the air and catches small live animals.
鵟（一種大型鷹）
noun · B2
In American English, a large bird that circles high in the sky and feeds on animals that are already dead, such as the turkey vulture or the black vulture.
禿鷲；美洲鷲