Not seething; calm and not bubbling with anger or agitation.
From Old English 'sēothan' (to boil) with the prefix 'a-' (not/without). The word evolved to describe a state opposite to seething, which originally meant literally boiling and came to mean churning with emotion.
While 'seethe' captures that feeling of anger bubbling under the surface, 'aseethe' is basically the zen master version—totally calm and un-bothered, though it's pretty rare to see this word used these days.
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