A homonym, on the strict school definition, is a word that is spelled the same and sounds the same as another word, but means something else — and often comes from a different history. Bear the animal and bear "to carry or put up with" are the stock example. Bank where you keep money and bank beside a river are another. Nothing in the letters or the sound warns you; only the rest of the sentence does. Though actually, this is one of the slipperiest labels English teachers use. Some textbooks say homonyms must match in both spelling and sound. Some allow a match in only one of those. Some use homonym for the whole messy family, and keep homograph for same spelling and homophone for same sound (two / too / to). Taiwan exam papers tend to want the strict pair: same look, same sound, different meaning. If your book uses the looser meaning, follow that book for the test, then remember that a linguist at the next desk might draw the lines differently. The word itself is a classroom tool, not something people say when they mix up bear in real life.

同音同形異義詞（嚴格定義；有的課本把「同音異義詞」也叫 homonym，易和 homophone 搞混）