One way to hold this word: an answer is owed, and it can be produced. What changes between the uses is who or what the answer is owed to — a question waiting on the page, or a person standing above you who can ask.
可以想成：有一個答案是欠著的，而且交得出來。兩個用法差的只是那個答案要交給誰。一邊是紙上那道等著被回答的題目。一邊是站在你上面、隨時可以開口問的人。字形上 answer 加 -able，就是「答得出來」，剩下的差別由介系詞去分。
From the word’s history
Wiktionary records the word as answer + -able, with -able coming through Latin -bilis and Old French -able, so the form literally means able to be answered.
維基詞典記錄的組成是 answer 加上 -able，而 -able 是從拉丁文 -bilis 經古法文 -able 進到英文的。所以字面上就是「可以被回答的」。這也解釋了為什麼比較貼字面的那個意思，反而不是字典排在前面的那個。
Wiktionary entry for answerable (kaikki:3f6f69a190036ae4:454992730:15241), etymology: From answer + -able.
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