Definition - A part of a phrase or clause that can be removed without the phrase or clause losing its sense.

For example, in the clause John lost the car yesterday, the word yesterday is an adjunct because it can be removed and the clause will still make sense.

However, in the sentence John won't go, there are no adjuncts because the clause is meaningless if any of the words are removed.

Etymology -
The word derives from the Latin adjunctus, the past participle of adjungere, join to.

Oxford English Dictionary -
Its first citation in this sense is from 1881:
"The basis and type of the Adverbial Adjunct is a substantive in an oblique case, used to limit or define the signification of a verb or adjective."
( Mason Eng. Gram. 149)

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