Dimensions

Just like the word "one", "dimension" has multiple meanings separate from each other. In "he is the one", it clearly has a completely different meaning than in "one plus one equals two".

When we're talking about the dimensions of an object in a space, it means the minimum points required to specify where that object is.

Let's suppose we're talking to each other face to face:

Me: "Where are you?"
You "Right in front of you!"

Now let's twist this a bit:

Me: Where were you?
You: I was in the bathroom.
Me: No, half an hour ago when I tried to call you.

You'll have a different answer in the second conversation after I have explained it further. The only thing that changes is in what point in time I'm trying to ask you about. That's why time is a dimension. You'd need it to answer me.

You: "Oh, at that time I was in the subway. I had no signal."