desiccant n.

active word-forming element in English and in many verbs inherited from French and Latin, from Latin de "down, down from, from, off; concerning" (see de), also used as a prefix in Latin, usually meaning "down, off, away, from among, down from," but also "down to the bottom, totally" hence "completely" (intensive or completive), which is its sense in many English words.

As a Latin prefix it also had the function of undoing or reversing a verb's action, and hence it came to be used as a pure privative — "not, do the opposite of, undo" — which is its primary function as a living prefix in English, as in defrost (1895), defuse (1943), de-escalate (1964), etc. In some cases, a reduced form of dis-.

early 15c. (Chauliac), of a medicine, "inducing or promoting dryness," from Late Latin siccativus "drying, siccative," from Latin siccatus, past participle of siccare "to dry, make dry; dry up," from siccus "dry, thirsty; without rain," from PIE root *seikw- "to flow out" (source also of Avestan hiku- "dry," Greek iskhnos "dry, withered," Lithuanian seklus "shallow," Middle Irish sesc "dry," Sanskrit sincati "makes dry"). The modern noun is attested by 1825; it also was a noun in Middle English.