The ordinal number matching the number 40; the position in a sequence after thirty-nine.
From Old English 'forty' + '-th' (ordinal suffix). The ordinal suffix '-th' creates ranking numbers: fourth, fifth, sixth, fortieth, fiftieth.
Ordinal numbers like 'fortieth' are so common we don't think about them, but they're proof that language builds complexity from simple rules—'forty' + a tiny suffix = a completely new word.
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