FromOld Norse því Proto-Germanic *hwī ( “ how, with what ” ) , with the initial h- replaced by the þ- from the forms of*sa
því
because ,for ,since Colossians 3:9Ljúgið ekki hver að öðrum,því þér hafið afklæðst hinum gamla manni með gjörðum hans. Do not lie to each other,since you have taken off your old self with its practices. því
( personal ) dative singular ofþað Icelandic personal pronouns singular first person second person third person masculine feminine neuter nominative ég eg ek † þú hann hún hon † ,hón † það þat † accusative mig mik † þig þik † hann hana það þat † dative mér þér honum hánum † henni því genitive mín þín hans hennar þess plural first person second person third person masculine feminine neuter nominative við þið þit † þeir þær þau accusative okkur ykkur þá þær þau dative okkur ykkur þeim þeim þeim genitive okkar ykkar þeirra þeirra þeirra
því...því
the ...the (when comparing)enþví meira sem hann blés,því þéttara vafði ferðamaðurinn kápunni að sér butthe more he blew,the tighter the traveller wrapped his coat around himself Possibly from the instrumental interrogativeProto-Germanic *hwī ( “ how, with what ” ) , with the initial h- replaced by the þ- from the forms of*sa ( “ that ” ) . CompareOld English þȳ ( “ by that; therefore; because; since ” ,instrumental case ofþæt ) . More atthe
því
dative singular ofþat Old Norse personal pronouns singular first person second person reflexive third person masculine feminine neuter nominative ek þú — hann hon hón hǫ́n þat accusative mik þik sik hann hana hána þat dative mér þér sér hánum hónum hǫ́num henni því genitive mín þín sín hans hennar þess dual first person second person reflexive nominative vit it þit — accusative okkr ykkr sik dative okkr ykkr sér genitive okkar ykkar sín plural first person second person reflexive third person masculine feminine neuter nominative vér ér þér — þeir þær þau accusative oss yðr sik þá þær þau dative oss yðr sér þeim þeim þeim genitive vár yðar yðvar sín þeira þeirra þeira þeirra þeira þeirra
Old Norse demonstrative pronouns
Icelandic:því Faroese:tí Norwegian:di ( dialectal ) Old Swedish:þȳ því notcomparable )
therefore ,for that reason 
