From Old High German *dag, northern variant of tag. The nominative case of this word became Luxembourgish Dag. The dative singular (and the plural) developed regularly into Do (dage > *dāe > *dōe > dō). Both forms then became distinct words with slightly different meanings.
Do m (uncountable)
- the bright time of the day (chiefly in adverbial constructions)
Am Do ginn d'Stroossen net beliicht.
- In the daytime, the streets are not lit.