Crossword Genius

The bitterness we all have (6)

Ross

I believe the answer is:

spleen

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'the bitterness' is the definition.
(thesaurus)

I don't understand the rest of the clue.

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(Other definitions for spleen that I've seen before include "Vent it to show anger" , "Bodily organ associated with bad humour" , "Internal organ - irascibility" , "Acrimony" , "Organ associated with ill humour" .)

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