MacBain suggests a relation to Ancient Greek θυμός (thumós, “soul, desire, passion”) and Lithuanian dūmas (“smoke”) (NB: Perhaps erroneously, MacBain glosses the Lithuanian as dumas (“thought”)). Regardless, if true, it would be from a derivative of Proto-Indo-European *dʰewh₂- (“smoke”).
From Old Irish dúil, dúl. MacBain relates this to Sanskrit धूलि (dhūli, “dust”) and Latin fūlīgō (“soot”), however Stokes suggests a relation to German zeugen (“to beget, to bear witness”) and Latin dūcō (“I pull, I guide”) to explain dialectic na dùil (“poor creatures!”) (cf. Irish dúil (“creature”)) and dùileag (“a term of affection for a girl”).
|Scottish Gaelic mutation|
|Note: Some of these forms may be hypothetical. Not every|
possible mutated form of every word actually occurs.