is Definition

be
verb, intr been, being, am (present tense), are, is, was (past tense), were

1. To exist or live.

Example: I think, therefore I am
Thesaurus: live, exist, endure, persist, subsist, breathe, abide, survive; Antonym: die, stop, disappear.
2. To occur or take place.

Example: Lunch is in an hour
Thesaurus: happen, occur, transpire, take place, come about.
3. To occupy a position in space.

Example: She is at home
4. To go.

Example: He's never been to Italy
5. To remain or continue without change.

Example: Let it be
6. (as a copula) used to link a subject and what is said about it.

Example: She is a doctor
Example: He is ill
7. Used with the infinitive form of a verb to express a possibility, command, intention, outcome, etc.

Example: if it were to rain
Example: We are to come tomorrow
Example: It was not to be

auxiliary verb

1. Used with a past participle to form a passive construction.

Example: The film was shown last night
2. Used with a present participle to form the progressive tenses.

Example: He was running

Idiom: be someone

To suit them
Example: That hat really isn't her.

Idiom: be that as it may

Although that may be true.

Idiom: the be-all and end-all

The only important issue or overriding aim.

Etymology: From Anglo-Saxon beon to live or exist, and Anglo-Saxon weran to be.

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I¹
i
noun Is, I's, i's

1. The ninth letter of the English alphabet.
2. An object or figure shaped like an I. See also I-beam.

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IS
abbreviation

1. IVR.
Iceland.

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is present tense of be