玄関のドアは開いていた。

entranceway; entry hall; vestibule; foyer; entryway; mud room

indicates possessive; nominalizes verbs and adjectives; substitutes for "ga" in subordinate phrases; (at sentence-end, falling tone) indicates a confident conclusion; (at sentence-end) indicates emotional emphasis; (at sentence-end, rising tone) indicates question

door (Western-style)

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

to open; to undo; to unseal; to unpack; to bloom; to unfold; to spread out; to open (for business, e.g. in the morning); to be wide (gap, etc.); to widen; to hold (meeting, etc.); to give; to open; to found (nation, dynasty, sect, etc.); to open (a new business); to set up; to establish; to start; to open (ports, borders, etc.); to open (an account); to open up (new land, path, etc.); to clear; to develop; to open (a file, etc.); to extract (root); to reduce (equation); to cut open (fish); to change (kanji into hiragana); to flare (e.g. skirt); to slacken (into a poor posture)