Alkali
The word "alkali" is derived from Arabic "al qalīy" (or "alkali"), meaning "the calcined ashes" (see calcination), referring to the original source of alkaline substances. A water-extract of burned plant ashes, called potash and composed mostly of potassium carbonate, was mildly basic. After heating this substance with calcium hydroxide ("slaked lime"), a far more strongly basic substance known as "caustic potash" (potassium hydroxide) was produced. Caustic potash was traditionally used in conjunction with animal fats to produce soft soaps, one of the caustic processes that rendered soaps from fats in the process of saponification, one known since antiquity. Plant potash lent the name to the element potassium, which was first derived from caustic potash, and also gave potassium its chemical symbol K (from the German name Kalium), which ultimately derived from alkali.
Alkali hydroxide
The alkali metal hydroxides are the strongest of all bases.The order of basicity increases down the group, i.e., LiOH is the least basic and CsOH, the most basic hydroxide. It is due to the property of bases to donate ion and due to small size and high lattice enthalpy of Li, it donates less and large size and low lattice enthalpy of Cs, Cesium hydroxide donates more ions than any other hydroxide. All the alkali metal hydroxides are white crystalline solids and dissolve freely in water with evolution of much heat.