I opened door with a key.

Meaning: This sentence describes the action of using a key to open a door.

Choice of Words: The sentence uses "opened" which means to make something accessible or visible. "Door" is a hinged, sliding, or revolving barrier at the entrance to a building, room, or vehicle. "Key" is a small piece of metal with notches that fits into a lock and operates it.

Alternative Expressions

I opened the door with a key.

Meaning: This sentence means that the person used a key to move the door so that there was a space through which to pass.

Choice of Words: I refers to the person who did the action, opened is a verb that means to move something so that there is a space or passage through which to pass, the is an article that specifies a particular thing, door is a noun that refers to a hinged, sliding, or revolving barrier at the entrance to a building, room, or vehicle, and with is a preposition that means using something as a means of accomplishing something, and key is a noun that refers to a small piece of metal with notches cut into it, used to operate a lock.

The key unlocked the door.

Meaning: This sentence means that the key was used to open the door.

Choice of Words: The is an article that specifies a particular thing, key is a noun that refers to a small piece of metal with notches cut into it, used to operate a lock, unlocked is a verb that means to open (a door, gate, or other entrance) with a key, and the is an article that specifies a particular thing, door is a noun that refers to a hinged, sliding, or revolving barrier at the entrance to a building, room, or vehicle.

I used the key to open the door.

Meaning: This sentence means that the person used the key to move the door so that there was a space through which to pass.

Choice of Words: I refers to the person who did the action, used is a verb that means to put something into service, the is an article that specifies a particular thing, key is a noun that refers to a small piece of metal with notches cut into it, used to operate a lock, to is a preposition that indicates the purpose of an action, open is a verb that means to move something so that there is a space or passage through which to pass, and the is an article that specifies a particular thing, door is a noun that refers to a hinged, sliding, or revolving barrier at the entrance to a building, room, or vehicle.

Related Expressions