Interpretatio germanica is the practice by the Germanic peoples of identifying Roman gods with the names of Germanic deities. According to Rudolf Simek, this occurred around the 1st century AD, when both cultures came into closer contact. Some evidence for interpretatio germanica exists in the Germanic translations of the Roman names for the days of the week:
- Sunday, the day of Sunnǭ (Old Norse: Sunna, Sól; Old English: Sunne; Old High German: Sunna), the sun (as female), was earlier the day of Sol, the sun (as male)
- Monday, the day of Mēnô (Máni; Mōna; Māno), the moon (as male), was earlier the day of Luna, the moon (as female)
- Tuesday, the day of Tīwaz (Týr; Tīw; Ziu), was earlier the day of Mars, god of war
- Wednesday, the day of Wōdanaz (Óðinn; Wōden; Wuotan), was earlier the day of Mercury, god of travelers and eloquence
- Thursday, the day of Þūraz/Þunraz (Þórr; Þunor; Donar), was earlier the day of Jupiter, god of thunder; Þunraz may elsewhere appear identified with the club-wielding Hercules
- Friday, the day of Frijjō (Frigg; Frīg; Frīja), was earlier the day of Venus, goddess of love
In most of the Romance languages, which derive from Latin, days of the week still preserve the names of the original Roman deities, such as the Italian for Tuesday, martedì (from the Latin Martis dies). This is also the case with Saturn in some West Germanic languages; such as the English "Saturday", the West Frisian Saterdei, the Low German Saterdag and the Dutch zaterdag all meaning Saturn's day.
Simek emphasizes the paucity of evidence and notes that comparison with Roman gods is insufficient to reconstruct ancient Germanic gods and equate them definitively with those of later Norse mythology.