The Collaborative International Dictionary of English v.0.48:

Motorize \Mo"tor*ize\ (m[=o]"t[~e]r*[imac]z), v. t. [Motor +
   -ize.]
   1. To substitute motor-driven vehicles, or automobiles, for
      the horses and horse-drawn vehicles of (a fire department,
      city, etc.). [archaic] -- Mo`tor*i*za"tion, n.
      [Webster 1913 Suppl.]

   2. to equip (a piece of machinery) with a motor.
      [PJC]

   3. to provide with automobiles or other motor vehicles; as, a
      motorized army division.

   Syn: mechanize.
        [PJC]

WordNet (r) 3.0 (2006):

motorize
    v 1: equip with a motor vehicle; "The police around here are not
         motorized and patrol the streets on horseback"
    2: equip with a motor; "motorized scooters are now the rage"
    3: equip with armed and armored motor vehicles; "mechanize
       armies" [syn: mechanize, mechanise, motorize,
       motorise]