One of the oldest IE words, with cognates from Sanskrit to Greek to Latin — five thousand years old and still in daily use.
A hinged, sliding, or revolving barrier at the entrance to a building, room, or vehicle. Also used figuratively for an opportunity or means of access.
From Old English 'duru' (door of a house) and 'dor' (large door, gate), from Proto-Germanic *durz, from PIE *dʰwer- (door, doorway, gate). This is one of the most ancient and stable words in the entire Indo-European family — cognates are found in nearly every branch, preserving both form and meaning across five millennia: Sanskrit 'dvāra' (door, gate), Avestan 'dvara-' (door), Greek 'thura' (door), Latin 'forēs' (double doors, via an earlier *dʰworēs with sound shift), Old Irish 'dorus' (door), Lithuanian 'durys' (doors), Old Church Slavonic 'dvьri' (doors), Armenian 'durn' (door), and Albanian 'derë' (door). The PIE form *dʰwer- is dual in most ancient languages
The words 'door,' 'foreign,' and 'forest' are all related through PIE '*dʰwer-' — 'foreign' comes from Latin 'foris' (outside the door), and 'forest' originally meant 'the outside land' beyond the settlement's doors.