The Collaborative International Dictionary of English v.0.48:

Habit \Hab"it\ (h[a^]b"[i^]t) n. [OE. habit, abit, F. habit, fr.
   L. habitus state, appearance, dress, fr. habere to have, be
   in a condition; prob. akin to E. have. See Have, and cf.
   Able, Binnacle, Debt, Due, Exhibit, Malady.]
   1. The usual condition or state of a person or thing, either
      natural or acquired, regarded as something had, possessed,
      and firmly retained; as, a religious habit; his habit is
      morose; elms have a spreading habit; esp., physical
      temperament or constitution; as, a full habit of body.
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   2. (Biol.) The general appearance and manner of life of a
      living organism. Specifically, the tendency of a plant or
      animal to grow in a certain way; as, the deciduous habit
      of certain trees.
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   3. Fixed or established custom; ordinary course of conduct;
      practice; usage; hence, prominently, the involuntary
      tendency or aptitude to perform certain actions which is
      acquired by their frequent repetition; as, habit is second
      nature; also, peculiar ways of acting; characteristic
      forms of behavior.
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            A man of very shy, retired habits.    --W. Irving.
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   4. Outward appearance; attire; dress; hence, a garment; esp.,
      a closely fitting garment or dress worn by ladies; as, a
      riding habit.
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            Costly thy habit as thy purse can buy. --Shak.
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            There are, among the statues, several of Venus, in
            different habits.                     --Addison.

   5. Hence: The distinctive clothing worn commonly by nuns or
      monks; as, in the late 1900's many orders of nuns
      discarded their habits and began to dress as ordinary lay
      women.
      [PJC]

   Syn: Practice; mode; manner; way; custom; fashion.

   Usage: Habit, Custom. Habit is a disposition or tendency
          leading us to do easily, naturally, and with growing
          certainty, what we do often; custom is external, being
          habitual use or the frequent repetition of the same
          act. The two operate reciprocally on each other. The
          custom of giving produces a habit of liberality;
          habits of devotion promote the custom of going to
          church. Custom also supposes an act of the will,
          selecting given modes of procedure; habit is a law of
          our being, a kind of "second nature" which grows up
          within us.
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                How use doth breed a habit in a man! --Shak.
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                He who reigns . . . upheld by old repute,
                Consent, or custom                --Milton.
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The Collaborative International Dictionary of English v.0.48:

Habit \Hab"it\ (h[a^]b"[i^]t), v. t. [imp. & p. p. Habited; p.
   pr. & vb. n. Habiting.] [OE. habiten to dwell, F. habiter,
   fr. L. habitare to have frequently, to dwell, intens. fr.
   habere to have. See Habit, n.]
   1. To inhabit. [Obs.]
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            In thilke places as they [birds] habiten. --Rom. of
                                                  R.
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   2. To dress; to clothe; to array.
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            They habited themselves like those rural deities.
                                                  --Dryden.
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   3. To accustom; to habituate. [Obs.]           --Chapman.
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WordNet (r) 3.0 (2006):

habit
    n 1: an established custom; "it was their habit to dine at 7
         every evening" [syn: habit, wont]
    2: (psychology) an automatic pattern of behavior in reaction to
       a specific situation; may be inherited or acquired through
       frequent repetition; "owls have nocturnal habits"; "she had a
       habit twirling the ends of her hair"; "long use had hardened
       him to it" [syn: habit, use]
    3: a distinctive attire worn by a member of a religious order
    4: the general form or mode of growth (especially of a plant or
       crystal); "a shrub of spreading habit"
    5: attire that is typically worn by a horseback rider
       (especially a woman's attire) [syn: habit, riding habit]
    6: excessive use of drugs [syn: substance abuse, drug abuse,
       habit]
    v 1: put a habit on

The Devil's Dictionary (1881-1906):

HABIT, n.  A shackle for the free.