One way to hold this word: something is able to make the crossing from one person to the next. Not whether it is good or bad, and not whether anyone wants it — only whether it can get across the gap. Once you have that picture, both uses are the same question asked about different cargo. Send an idea across and the word is about teaching and writing. Send an illness across and the word is about public health. The word itself does not change; only what is travelling does.
From the word’s history
From Old French communicable, from Latin communicabilis — the same root as communicate — with the ending -able, meaning able to be done to it. So the parts spell out able to be shared, which is exactly the crossing in the core picture.
來自古法文 communicable，再往前是拉丁文 communicabilis，跟 communicate 同一個字根；字尾 -able 是「可以被…的」。所以零件拼起來就是「可以被分享出去的」，正好就是核心畫面裡的那個過渡。
Wiktionary entry supplied in this packet (kaikki:3f6f69a190036ae4:1410459827): From Old French communicable, Latin communicabilis.
登入就可以看每一支怎麼連回核心畫面。