The Japanese word for saw is nokogiri. The -giri is transparently a nominalized and voiced form of the root /kir/, "cut". So what is the noko?

My first guess was that it was somehow related to /ki/, "tree/wood", which regularly appears as /ko/ in compound words like kogarashi*, as discussed here. There's even a word noki, meaning a tree standing in a field (no), and a homophone (homophonic status in OJ times uncertain) that means "eave". Any of these things, a saw can cut. The only remaining question is which it was originally. Case closed.

But no! A trip to the dictionary reveals that the word was originally nohogiri. Ki, wood, is irrelevant. What, then, is a noho?

Sadly, no-one knows for sure. Many have proposed some relation to the /nob/ in modern words like nobiru ("stretch") and nobasu ("extend [something]"), etc., but this theory is undermined by the fact that /nob/ isn't found as /noh/ anywhere else. To patch this leak, some insert a /ha/ ("edge", "tooth") in between the /nob/ and /kiri/ and implicitly invoke a poorly-understood Blender Principle to get the final word -- but you're asking for an awful lot of sound change at that point, finalized and traceless before writing began.

All this etymological opacity, plus the fact that the referent is non-obvious technology, obviously raises the possibility that the word's origins lie outside of the Yamatosphere altogether. If this were the case, the variant noko might be not an abbreviation but rather a descendent of the original word itself, with nokogiri just meaning "noko (or noho, nopo, etc.) cutter".

In from the western ports they rode, reins clutched in one fist and carpentry tools held high. O fierce ones, I ask you then: What is best in life? To build wooden dwellings, to plane them smooth -- to carpet the land in sawdust and hear the lamentation of the native construction industry. That is what is best!