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In reading a book on the geology of our planet, the term "trap" was finally explained in terms I can comprehend: a massive accumulation of basalt resulting from extended volcanism. Usually found in the plural, the two most often (in my experience) mentioned examples are the Deccan Traps (in India) and the Siberian Traps.

Etymologically related to Swedish "trappa" (meaning steps or staircase), this doesn't seem to be related to the usual English meaning (verb or noun). Or is it?

Because they have a stepped appearance, these volcanic outcroppings were called such: traps. Now, how we got from trap to staircase, or from staircase to trap, I don't quite follow.

But Slava, you're still referring to the geologic trap.

I was (and am) wondering about an object like a mousetrap or a grease trap in a sink, or a fur trapper (a person), or a kind of pony cart, or even a trapdoor. (Well, that last very often leads to steps, but if I go out to trap a muskrat, I'm not making the connection,)

Oh, and I'm guessing (since "trappa" means "steps" in Swedish), the geologists responsible for the name may have been Scandinavian.

I guess I wasn't clear in my wondering; the trap I had in mind was the kind you trip. I guess you can trip up and down stairs, which could make them a dangerous trap for the clumsy, but how did something that means staircase come to mean the ловушка (lovushka) you fall into?

From an ancient past participle of trip, perhaps?

The connection seems to be "something on/into which one steps":

http://etymonline.com/word/trap