Lakhwiya, لخويه.

You'll never find it.

It comes from brother اﻷخ, brothers, brotherhood ....

It's in our local dialect of Arabic. It's what we called the people who used to ride around the cities to protect them. It's an old word.

We tend to pronounce ال or "the" lighter than in Standard Arabic or other dialects, so when they started writing local words, they omitted the first letter, and wrote them phonetically, as close as possible to what we would pronounce the word.

You'll be much more puzzled if you look at some of the newer street names, they are being named in very obscure (to a non-Qatari, or to the newer generations of Qataris) cultural references and words, like we have a word that means "The low area between two high areas where the rain has poured as seen from above" (it's in one of the street names, and it's a single word)