Definition -
(1) A part of a sentence that itself includes a subject and a predicate.
(2) A short sentence.

Example -
I ate it because I wanted to eat it.
( I wanted to eat it is a clause because it contains
(1) the subject I and
(2) the predicate wanted to eat it.)

Etymology -
The word derives via Old French and Medieval Latin from the Latin clausula, the close of a sentence.

Oxford English Dictionary -
The word's first citation in its grammatical sense is from 1865:
"A phrase is a combination of words without a predicate; a clause is a term of a sentence containing a predicate within itself; as, a man who is wise."
(Dalgleish Gram. Analysis 15)

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