From now on; starting from this time in the future.
From Middle English 'hences' (from here) + 'forward' (Old English 'foreweard'). Originally meant 'forward from this place' but evolved to mean 'forward in time' from the 14th century onward.
Old-fashioned sounding words like 'henceforward' are actually quite logical—'hence' meant 'from here' (literally a place), so adding 'forward' created 'from here forward,' which we naturally extended to mean 'from now forward' in time.
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