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A Latin term coined by Arnold Pick in 1891, first used in German and later adopted into English. From the Latin dēmentia (“madness; insanity”) + praecox (“premature; untimely”, whence English precocious), together meaning “untimely madness” or “premature dementia”. Here, dēmentia carries the connotation of senile dementia.
Etymology from Wiktionary, CC BY-SA 4.0.