in \in\, adv.
   1. 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.
      1913 webster

            their vacation . . . falls in so pat with ours.
                                                  --lamb.
      1913 webster

   note: the sails of a vessel are said, in nautical language,
         to be in when they are furled, or when stowed. in
         certain cases in has an adjectival sense; as, the in
         train i. e., the incoming train; compare up grade,
         down grade, undertow, afterthought, etc.
         1913 webster

   2. law with privilege or possession; -- used to denote a
      holding, possession, or seisin; as, in by descent; in by
      purchase; in of the seisin of her husband. --burrill.
      1913 webster

   in and in breeding. see under breeding.

   in and out naut., through and through; -- said of a
      through bolt in a ship's side. --knight.

   to be in, to be at home; as, mrs. a. is in.

   to come in. see under come.
      1913 webster
see also:
in and in breeding breeding in and out to be in to come in come