真的會痛
這一家就是字面意思本身，也是另外兩個用法借東西的源頭。
r · B2
In a way that hurts, or in a way that shows the person or animal doing it is in pain.
疼痛地
核心畫面
Start with the body: a sore throat, a hurt knee, an old dog getting up. Painfully is how an action goes when it hurts to do it, and when anyone watching can see that it hurts. English then lends that feeling out. It lends it to degree — painfully shy, painfully slow, painfully obvious — where nothing hurts but the speaker wants you to feel the strain. And it lends it to effort — painfully acquired, painfully rebuilt — where the cost is in the work, paid a little at a time.
先從身體開始：喉嚨痛、膝蓋傷了、老狗慢慢從窩裡站起來。painfully 就是「做起來會痛」的那個樣子，而且旁邊的人…更多收起
先從身體開始：喉嚨痛、膝蓋傷了、老狗慢慢從窩裡站起來。painfully 就是「做起來會痛」的那個樣子，而且旁邊的人看得出來。英文後來把這個感覺借了出去。一邊借給程度：painfully shy、painfully slow、painfully obvious，沒有人真的痛，但說話的人要你感覺到那股難受。一邊借給過程：painfully acquired、painfully rebuilt，痛的是花掉的力氣，一點一點付出去的。可以想成同一種疼，換了地方落下。From the word’s history
Painfully comes from painful plus -ly, going back to Middle English peinfully. Painful is pain plus -ful, so the adverb starts life meaning simply 'in a way full of pain' — which is still the literal sense at the centre.
painfully 由 painful 加 -ly 而來，往上追到中古英語的 peinfully；而 painful 又是 pain 加 -ful。所以這個副詞一開始的意思就是「以充滿痛的方式」，也就是今天最字面的那一個用法，其他兩個都是從它借出去的。
Wiktionary entry 'painfully' (source_ref kaikki:3f6f69a190036ae4:1025912330:6868): 'From Middle English peinfully, paynefully, equivalent to painful + -ly.'
Two branches
把痛借來講程度和辛苦
痛從身體移到感受和過程。沒有人受傷，但說話的人要你感覺到那股讓人不舒服的強度或代價。
r · B2
Very — used before a word describing something bad, weak, or unwanted, to say that it is true to a degree that is hard to watch, hard to sit through, or hard to admit.
極其／令人難受地