simple past tense and past participle of treat
"After they treated him to dinner, he finally felt like paying his own way next time."
In plain English: Treated means to give someone medical care or to act toward them in a specific way.
"The restaurant treated us to dinner in celebration of her promotion."
subjected to a physical (or chemical) treatment or action or agent
"the sludge of treated sewage can be used as fertilizer"
"treated timbers resist rot"
"treated fabrics resist wrinkling"
given medical care or treatment
"a treated cold is usually gone in 14 days; if left untreated it lasts two weeks"
Derived from the Old French traiter, which meant to draw, drag, or treat, the past tense form entered English via Middle English with the original sense of handling or managing something. It evolved to signify dealing with an illness or subject matter through specific actions or remedies.