Þ ū n res d æ g ▁and ▁Middle ▁English ▁Th ures day ▁( with ▁loss ▁of ▁- n -, ▁first ▁in ▁northern ▁dialect s , ▁from ▁influence ▁of ▁Old ▁Nor se ▁ Þ ó rs d agr ) ▁meaning ▁" Th or ' s ▁Day ". ▁It ▁was ▁named ▁after ▁the ▁Nor se ▁god ▁of ▁Th under , ▁Thor . ▁ ▁Th un or , ▁Don ar ▁( G erman , ▁Don ner stag ) ▁and ▁Thor ▁are ▁derived ▁from ▁the ▁name ▁of ▁the ▁German ic ▁god ▁of ▁th under , ▁Th un raz , ▁equivalent ▁to ▁Jup iter ▁in ▁the ▁interpret atio ▁rom ana . ▁ ▁In ▁most ▁Rom ance ▁languages , ▁the ▁day ▁is ▁named ▁after ▁the ▁Roman ▁god ▁Jup iter , ▁who ▁was ▁the ▁god ▁of ▁sky ▁and ▁th under . ▁ ▁In ▁Latin , ▁the ▁day ▁was ▁known ▁as ▁I ovis ▁Dies , ▁" J up iter ' s ▁Day ". ▁ ▁In ▁Latin , ▁the ▁gen itive ▁or ▁possess ive ▁case ▁of ▁Jup iter ▁was ▁I ovis / J ovis ▁and ▁thus ▁in ▁most ▁Rom ance ▁languages ▁it ▁became ▁the ▁word ▁for ▁Th urs day : ▁Italian ▁gi oved ì , ▁Spanish ▁j ue ves , ▁French ▁je udi , ▁S ardin ian ▁j ò via , ▁Catal an ▁di j ous , ▁Gal ician ▁x ov es ▁and ▁Roman ian ▁jo i . ▁This ▁is ▁also ▁reflected ▁in ▁the ▁p - C elt ic ▁Wel sh ▁dy dd ▁I au . ▁ ▁The ▁ast ro log