一頁的底部那一條
走的是 foot 的「底部」那條線：這裡的 footer 是一個位置，不是一個人。
noun · B1
A line or small block of text that appears at the bottom of every page of a document or a website, often showing the page number, the date, the file name or the name of the company.
頁尾／頁腳
核心畫面
One way to hold this footer: it is foot plus -er, and foot has two everyday jobs. A foot is the bottom of something, so the foot of a page is its lowest edge, and the footer is the strip that lives down there and repeats on every page. A foot is also the thing you stand on and measure with, so a foot of length is thirty and a foot is left or right. Add -er to that side and the word stops naming a place and starts labelling a person or a thing by a fact about feet: how many of them tall, or which one they kick with.
這個 footer 可以想成 foot 加上 -er，而 foot 在日常英文裡做兩份工作。第一份是「底部」：一頁的…更多收起
這個 footer 可以想成 foot 加上 -er，而 foot 在日常英文裡做兩份工作。第一份是「底部」：一頁的 foot 就是最下緣，所以 footer 是待在那裡、每頁都重複出現的那一條。第二份是「腳」：腳被拿來量長度，一英尺大約三十公分；腳也分左右。接上 -er 之後，這個字就不再指位置，而是變成一個標籤，用跟腳有關的事實來稱呼一個人或一樣東西——高幾英尺，或者習慣用哪一隻腳。From the word’s history
Wiktionary gives this footer as Middle English footer, equivalent to foot plus -er, and points to foot as used in printing for the bottom of a page.
維基詞典說這個 footer 來自中古英文 footer，等於 foot 加上 -er，並且要讀者對照印刷用語裡指「一頁底部」的 foot。
Wiktionary entry 'footer' (noun, etymology 1), packet source_ref kaikki:3f6f69a190036ae4:1113920181
Two branches
用腳的事實給人事物貼標籤
走的是 foot 的另一條線：腳是量長度的單位，也分左右。這一族的 footer 一定接在別的字後面，自己不能單獨站。
noun · B2
Used after a number, with a hyphen, to name someone or something that measures that many feet: a six-footer is a person six feet tall, and an eighteen-footer is a boat eighteen feet long.
…英尺高／長的人或物