simple (adj.)

c. 1200, "free from duplicity, upright, guileless; blameless, innocently harmless," also "ignorant, uneducated; unsophisticated; simple-minded, foolish," from Old French simple (12c.) "plain, decent; friendly, sweet; naive, foolish, stupid," hence "wretched, miserable," from Latin simplus from PIE compound *sm-plo-, from root *sem- (1) "one; as one, together with" + *-plo- "-fold."

Sense of "free from pride, humble, meek" is mid-13c. As "consisting of only one substance or ingredient" (opposite of composite or compounded) it dates from late 14c.; as "easily done" (opposite of complicated) it dates from late 15c.

From mid-14c. as "unqualified; mere; sheer;" also "clear, straightforward; easily understood." From late 14c. as "single, individual; whole." From late 14c. of clothing, etc., "modest, plain, unadorned," and of food, "plain, not sumptuous." In medicine, of fractures, etc., "lacking complications," late 14c. As a law term, "lacking additional legal stipulations, unlimited," from mid-14c.

In Middle English with wider senses than recently, such as "inadequate, insufficient; weak, feeble; mere; few; sad, downcast; mournful; of little value; low in price; impoverished, destitute;" of hair, "straight, not curly." As noun, "an innocent or a guileless person; a humble or modest person" (late 14c.), also "an uncompounded substance." From c. 1500 as "ignorant people."

updated on October 04, 2018

Definitions of simple from WordNet
simple (adj.)
apart from anything else; without additions or modifications;
the simple truth
the simple passage of time was enough
Synonyms: bare / mere
simple (adj.)
having few parts; not complex or complicated or involved;
simple mechanisms
a simple problem
a simple design
a simple substance
simple (adj.)
easy and not involved or complicated;
a simple game
Synonyms: elementary / uncomplicated / unproblematic
simple (adj.)
exhibiting childlike simplicity and credulity;
Synonyms: childlike / wide-eyed / round-eyed / dewy-eyed
simple (adj.)
lacking mental capacity and subtlety;
Synonyms: dim-witted / simple-minded
simple (adj.)
(botany) of leaf shapes; of leaves having no divisions or subdivisions;
Synonyms: unsubdivided
simple (adj.)
her black dress--simple to austerity
a simple country schoolhouse
simple (n.)
any herbaceous plant having medicinal properties;
simple (n.)
a person lacking intelligence or common sense;
Synonyms: simpleton
Etymologies are not definitions. From, not affiliated with etymonline.