The etymology of the word antonym integrates the voices "name" and "opposite"., which is teaching for understanding that you it's words that express contrary ideas among themselves. It is common to find antonyms which are names (e.g., love-hate), they are also abundant in the adjectives (e.g., high/low, long, veloz-lento) as well as in verbs (e.g., upload - download). But not all words have nor need an antonym. What, for example, the antonym of Chair, or book, etc.? In principle we can think the same voice, water, although one hears or reads there "waterproof", used in cases such as case waterproof, cellular, or mobile waterproof, waterproof camera, waterproof laptop..., but note that the idea that is conveyed in these cases is that these articles are resistant to the effect of the water, not the that mean the opposite of the word water itself.
