21-letter words containing m, e, l, i, o, r
- well-ordering theorem — the theorem of set theory that every set can be made a well-ordered set.
- william of malmesbury — William of, William of Malmesbury.
- william the conqueror — ("the Conqueror") 1027–87, duke of Normandy 1035–87; king of England 1066–87 (son of Robert I, duke of Normandy).
- wilson's storm petrel — a small petrel, Oceanites oceanicus, that breeds in the Southern Hemisphere but ranges into the North Atlantic and Pacific oceans.
- worth someone's while — worth someone's time, consideration, etc.; profitable in some way
- xilinx netlist format — (language, electronics) (XNF) A Hardware Description Language for electronic circuit design, developed by Xilinx, Inc..
- yellow mercuric oxide — a slightly crystalline, water-soluble, poisonous compound, HgO, occurring as a coarse, orange-red powder (red mercuric oxide) or as a fine, orange-yellow powder (yellow mercuric oxide) used chiefly as a pigment in paints and as an antiseptic in pharmaceuticals.
- yellow-fever mosquito — a mosquito, Aedes aegypti, that transmits yellow fever and dengue.
- your mileage may vary — (jargon) (YMMV) The disclaimer American car manufacturers attached to EPA mileage ratings. A humourous way of saying that the thing under discussion will not necessarily give you the same results as the author. Often used to convey the hardware dependence of Unix freeware distributions.
- zero-emission vehicle — a vehicle, as an automobile, that does not directly produce atmospheric pollutants. Abbreviation: ZEV.