I'm a U.S. native English speaker. I was chatting with a language partner who is dealing with some scientific datasets obtained from locations on the side of a hill. The two datasets were named (not by her) "up" and "bottom," which made me laugh, and I was trying to explain why.

It really got me to thinking about the mysteries of the range of meanings and usage of some very common English words. 

The opposite of <em>up</em> is <em>down</em>. 

But the opposite of <em>upper</em> is not <em>downer</em>, it's <em>lower</em>. 

However, if someone asked me out of the blue "What's the opposite of <em>lower</em>," I think I'd say <em>higher</em>, not <em>upper</em>. 

The pairs "high/low," "top/bottom," "up/down," and "upper/lower" have meanings that I understand easily but have difficulty defining.

A carton of fragile items can say "this side up," but can't say "this side top" or "this side high."

You can speak of the "bottom" and "top" of a hill, but when you are speaking of a mountain, for some reason the vocabulary changes a little. You could speak of the "top" of a mountain, but would be more likely to say <em>peak</em> or <em>summit</em>. I don't think you can speak of the "bottom" of a mountain--it would be the <em>base</em>. And yet, you could speak about finally getting to the "bottom" of a long, winding mountain road. 

There is such a word as <em>mountaintop</em>, but not "mountainbottom" or "mountainbase."

I can feel something "from the bottom of my heart," but not the "top of my heart." I can give an opinion "off the top of my head," but not from the "bottom of my head."

Your thoughts?