The Collaborative International Dictionary of English v.0.48:

Ho \Ho\, pron.
   Who. [Obs.]

   Note: In some Chaucer MSS. Ho

The Collaborative International Dictionary of English v.0.48:

Ho \Ho\, Hoa \Hoa\, n. [See Ho, interj., 2.]
   A stop; a halt; a moderation of pace.
   [1913 Webster]

         There is no ho with them.                --Decker.

The Collaborative International Dictionary of English v.0.48:

Ho \Ho\, prop. n. (Chem.)
   The chemical symbol for Holmium.
   [PJC] Ho

The Collaborative International Dictionary of English v.0.48:

Ho \Ho\, Hoa \Hoa\ (h[=o]), interj. [Cf. F. & G. ho.]
   1. Halloo! attend! -- a call to excite attention, or to give
      notice of approach. "What noise there, ho?" --Shak. "Ho!
      who's within?" --Shak.
      [1913 Webster]

   2. [Perhaps corrupted fr. hold; but cf. F. hau stop! and E.
      whoa.] Stop! stand still! hold! -- a word now used by
      teamsters, but formerly to order the cessation of
      anything. [Written also whoa, and, formerly, hoo.]
      [1913 Webster]

            The duke . . . pulled out his sword and cried "Hoo!"
                                                  --Chaucer.
      [1913 Webster]

            An herald on a scaffold made an hoo.  --Chaucer.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Hydroxyl \Hy*drox"yl\, n. [Hydro-, 2 + oxygen + -yl.] (Chem.)
   A compound radical, or unsaturated group, HO, consisting of
   one atom of hydrogen and one of oxygen. It is a
   characteristic part of the hydrates, the alcohols, the oxygen
   acids, etc.
   [1913 Webster]