Past tense of drone: spoke in a dull, monotonous voice, or made a low humming sound continuously.
From Old English 'dran' (to vibrate/hum) combined with regular English past tense '-ed'. The connection to bees' buzzing led to the metaphorical use for monotonous human speech.
The word 'droned' perfectly captures that feeling when a teacher's voice becomes background noise—your brain literally can't keep up with such rhythmic, emotionless speech!
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