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Old English swefn (cognate)
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Ancient Greek ὕπνος (cognate)
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Proto-Indo-Iranian *swap- (root)
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Proto-Indo-Iranian *swápnas (inherited)
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Proto-Indo-Aryan *swap- (root)
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Proto-Indo-European *swep- (root)
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Proto-Indo-European *swépnos (inherited)
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Proto-Indo-European *swep- (mention)