The Collaborative International Dictionary of English v.0.48:

Mustard \Mus"tard\, n. [OF. moustarde, F. moutarde, fr. L.
   mustum must, -- mustard was prepared for use by being mixed
   with must. See Must, n.]
   1. (Bot.) The name of several cruciferous plants of the genus
      Brassica (formerly Sinapis), as white mustard
      (Brassica alba), black mustard (Brassica Nigra),
      wild mustard or charlock (Brassica Sinapistrum).
      [1913 Webster]

   Note: There are also many herbs of the same family which are
         called mustard, and have more or less of the flavor of
         the true mustard; as, bowyer's mustard (Lepidium
         ruderale); hedge mustard (Sisymbrium officinale);
         Mithridate mustard (Thlaspi arvense); tower mustard
         (Arabis perfoliata); treacle mustard (Erysimum
         cheiranthoides).
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   2. A powder or a paste made from the seeds of black or white
      mustard, used as a condiment and a rubefacient. Taken
      internally it is stimulant and diuretic, and in large
      doses is emetic.
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   Mustard oil (Chem.), a substance obtained from mustard, as
      a transparent, volatile and intensely pungent oil. The
      name is also extended to a number of analogous compounds
      produced either naturally or artificially.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Tower \Tow"er\, n. [OE. tour,tor,tur, F. tour, L. turris; akin
   to Gr. ?; cf. W. twr a tower, Ir. tor a castle, Gael. torr a
   tower, castle. Cf. Tor, Turret.]
   1. (Arch.)
      (a) A mass of building standing alone and insulated,
          usually higher than its diameter, but when of great
          size not always of that proportion.
      (b) A projection from a line of wall, as a fortification,
          for purposes of defense, as a flanker, either or the
          same height as the curtain wall or higher.
      (c) A structure appended to a larger edifice for a special
          purpose, as for a belfry, and then usually high in
          proportion to its width and to the height of the rest
          of the edifice; as, a church tower.
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   2. A citadel; a fortress; hence, a defense.
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            Thou hast been a shelter for me, and a strong tower
            from the enemy.                       --Ps. lxi. 3.
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   3. A headdress of a high or towerlike form, fashionable about
      the end of the seventeenth century and until 1715; also,
      any high headdress.
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            Lay trains of amorous intrigues
            In towers, and curls, and periwigs.   --Hudibras.
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   4. High flight; elevation. [Obs.] --Johnson.
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   Gay Lussac's tower (Chem.), a large tower or chamber used
      in the sulphuric acid process, to absorb (by means of
      concentrated acid) the spent nitrous fumes that they may
      be returned to the Glover's tower to be reemployed. See
      Sulphuric acid, under Sulphuric, and Glover's tower,
      below.

   Glover's tower (Chem.), a large tower or chamber used in
      the manufacture of sulphuric acid, to condense the crude
      acid and to deliver concentrated acid charged with nitrous
      fumes. These fumes, as a catalytic, effect the conversion
      of sulphurous to sulphuric acid. See Sulphuric acid,
      under Sulphuric, and Gay Lussac's tower, above.

   Round tower. See under Round, a.

   Shot tower. See under Shot.

   Tower bastion (Fort.), a bastion of masonry, often with
      chambers beneath, built at an angle of the interior
      polygon of some works.

   Tower mustard (Bot.), the cruciferous plant Arabis
      perfoliata.

   Tower of London, a collection of buildings in the eastern
      part of London, formerly containing a state prison, and
      now used as an arsenal and repository of various objects
      of public interest.
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