To lie down in a reclining position; to recline or lean.
From Old English 'cumbel' or related to 'cumber' (to lie down, encumber). The prefix 'a-' indicates a state or condition. This is an archaic word rarely used in modern English, surviving primarily in historical texts and regional dialects. The original sense related to taking up space or lying heavily.
This is one of those wonderfully weird English words that almost nobody uses anymore, but it perfectly captures that feeling of flopping down on a couch after a long day—literally meaning to lie down heavily or recline messily.
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