Once upon a time, back in the days of black-and-white television, I heard the word "watermelons" exclaimed in a TV program with reference to a lovely young woman's ample bosom. But I'm not sure this qualifies as a figure of speech.
"Her laughter was as refreshing and sweet as a watermelon on a hot summer's day."
Watermelons contain water of 92%. A "Watermelon Speech" is a speech that isn't solid. It lasts as long as a watermelon. It comes and goes and doesn't leave an effect.
comparing something using like, as , or than
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A figure of speech
Hyperbole means to exaggerate in the style of a figure of speech.
simile a comparison using like or as
A figure of speech such as "He is as strong as an ox" is called a simile. It is a literary device that compares two different things using the words "like" or "as".
metaphor
the watermelon big like a dick
figure of speech according to categories
The Tagalog term for "figure of speech" is "larawang-diwa."
"Black as coal" is a simile.