/ dɪˈmentɪd; NAmE / adjective
1.
( especially BrE ) behaving in a crazy way because you are extremely upset or worried :
I've been nearly demented with worry about you.
2.
( old-fashioned or medical ) having a mental illness
► de·men·ted·ly adverb
••
WORD ORIGIN
mid 17th cent.: past participle of earlier dement drive mad , from Old French dementer or late Latin dementare , from demens out of one's mind.