Feeling angry and resentful, usually because of something unfair or hurtful that happened to you.
From 'em-' (to cause) + 'bitter'. The metaphorical sense of 'bitter' meaning resentful comes from the physical taste and has been used since Middle English to describe sour emotions.
Your mouth literally tastes bitter when you're upset—scientists found that anger and bitterness trigger the same taste receptors, so the word perfectly captures how emotions and sensations are connected!
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