in | English to English Dictionary

English to English

(/I/n )

A prefix from Eng. prep. in, also from Lat. prep. in, meaning in, into, on, among; as, inbred, inborn, inroad; incline, inject, intrude. In words from the Latin, in- regularly becomes il- before l, ir- before r, and im- before a labial; as, illusion, irruption, imblue, immigrate, impart. In- is sometimes used with an simple intensive force.(preposition)

source: webster1913
The specific signification of in is situation or place with respect to surrounding, environment, encompassment, etc. It is used with verbs signifying being, resting, or moving within limits, or within circumstances or conditions of any kind conceived of as limiting, confining, or investing, either wholly or in part. In its different applications, it approaches some of the meanings of, and sometimes is interchangeable with, within, into, on, at, of, and among.(preposition)

source: webster1913

to or toward the inside of(adv.all)

Example:
Come in.
Smash in the door.

source: wordnet30
Not out; within; inside. In, the preposition, becomes an adverb by omission of its object, leaving it as the representative of an adverbial phrase, the context indicating what the omitted object is; as, he takes in the situation (i. e., he comprehends it in his mind); the Republicans were in (i. e., in office); in at one ear and out at the other (i. e., in or into the head); his side was in (i. e., in the turn at the bat); he came in (i. e., into the house).(adverb)

source: webster1913