Noun

(uncountable) Capacity of mind, especially to understand principles, truths, facts or meanings, acquire knowledge, and apply it to practice; the ability to learn and comprehend.

* 1912 , (Edgar Rice Burroughs), (Tarzan of the Apes), Chapter 5

Not so, however, with Tarzan, the man-child. His life amidst the dangers of the jungle had taught him to meet emergencies with self-confidence, and his higher intelligence resulted in a quickness of mental action far beyond the powers of the apes.

* {{quote-magazine, date=2013-07-19, author= Ian Sample

, volume=189, issue=6, page=34, magazine=(The Guardian Weekly) , title= Irregular bedtimes may affect children's brains , passage=Irregular bedtimes may disrupt healthy brain development in young children, according to a study of intelligence and sleeping habits.  ¶ Going to bed at a different time each night affected girls more than boys, but both fared worse on mental tasks than children who had a set bedtime, researchers found.}}

(countable) An entity that has such capacities.

* Tennyson

The great Intelligences fair / That range above our mortal state, / In circle round the blessed gate, / Received and gave him welcome there.

(uncountable) Information]], usually secret, about the enemy or about hostile [[activity, activities.

(countable) A political or military department, agency or unit designed to gather information, usually secret, about the enemy or about hostile activities.

(dated) Acquaintance; intercourse; familiarity.

* Clarendon

He lived rather in a fair intelligence than any friendship with the favourites.

Noun

(en noun)

A strand of yarn etc. as used to guide one through a labyrinth; something which points the way, a guide.

* 1897 , Henry James, What Maisie Knew :

she had even had in the past a small smug conviction that in the domestic labyrinth she always kept the clue .

Information which may lead one to a certain point or conclusion.

An object or a kind of indication which may be used as evidence.

(slang) Insight or understanding ("to have a clue [about]" or "to have clue". See have a clue, clue stick)