The Collaborative International Dictionary of English v.0.48:

Mono- \Mon"o-\, Mon- \Mon-\ [Gr. ?.]
   A prefix signifying one, single, alone; as, monocarp,
   monopoly; (Chem.) indicating that a compound contains one
   atom, one radical, or one group of that to the name of which
   it is united; as, monoxide, monosulphide, monatomic, etc.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Mon- \Mon-\
   Same as Mono-.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Mon \Mon\ (m[o^]n), n. [Jap., usually translated as crest.]
   (Japan)
   The badge of a family, esp. of a family of the ancient feudal
   nobility. The most frequent form of the mon is circular, and
   it commonly consists of conventionalized forms from nature,
   flowers, birds, insects, the lightnings, the waves of the
   sea, or of geometrical symbolic figures; color is only a
   secondary character. It appears on lacquer and pottery, and
   embroidered on, or woven in, fabrics. The imperial
   chrysanthemum, the mon of the reigning family, is used as a
   national emblem. Formerly the mon of the shoguns of the
   Tokugawa family was so used.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

Mon
    n 1: the second day of the week; the first working day [syn:
         Monday, Mon]
    2: a member of a Buddhist people living in Myanmar and adjacent
       parts of Thailand
    3: the Mon-Khmer language spoken by the Mon