21-letter words containing a, l, o, s
- william of malmesbury — William of, William of Malmesbury.
- x-ray crystallography — the determination of the structure of a crystal by the use of x-ray diffraction.
- xilinx netlist format — (language, electronics) (XNF) A Hardware Description Language for electronic circuit design, developed by Xilinx, Inc..
- yellow lady's-slipper — a showy orchid, Cypripedium calceolus, of eastern North America, having purple-tinged yellow flowers with an inflated lip petal.