Set on fire or burning; in a state of being ignited or kindled; aflame.
From Middle English 'a-' (on, at) + 'kindle' (to set fire); this is a compound prefix meaning 'in a state of' combined with the verb kindle.
English used to love this 'a-' prefix to show states of being—akindle, ablaze, alight—it's like a shorthand for 'become this thing,' and it's why 'alive' originally meant 'in life'!
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