The Collaborative International Dictionary of English v.0.48:

Kotow \Ko*tow"\, n. [Chinese, knock head.]
   Same as kowtow, the more common spellings. [China] [Also
   spelled kowtow.] --S. W. Williams.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Kotow \Ko*tow"\, v. i. [imp. & p. p. Kotowed; p. pr. & vb. n.
   Kotowing.]
   1. To perform the kotow. Now usually spelled kowtow. [Also
      spelled kowtow.]
      [1913 Webster]

   2. To defer to another in a servile or humiliating manner; to
      act obsequiously.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Kowtow \Kow*tow"\, n. [Chinese, knock head.]
   The prostration made by mandarins and others to their
   superiors, either as homage or worship, by knocking the
   forehead on the ground; same as Kotow. There are degrees in
   the rite, the highest being expressed by three knockings.
   [China] [Also spelled kotow.] --S. W. Williams.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Kowtow \Kow*tow"\, v. i. [imp. & p. p. Kowtowed; p. pr. & vb.
   n. Kowtowing.]
   To perform the kowtow. Same as Kotow
   [1913 Webster]

         I have salaamed and kowtowed to him.     --H. James.
   [1913 Webster]

   2. To defer to another in a servile or humiliating manner; to
      act obsequiously.

   Syn: kotow.
        [PJC]

WordNet (r) 3.0 (2006):

kowtow
    n 1: a former Chinese custom of touching the ground with the
         forehead as a sign of respect or submission [syn: kowtow,
         kotow]
    v 1: bend the knees and bow in a servile manner [syn: scrape,
         kowtow, genuflect]
    2: try to gain favor by cringing or flattering; "He is always
       kowtowing to his boss" [syn: fawn, toady, truckle,
       bootlick, kowtow, kotow, suck up]

Moby Thesaurus II by Grady Ward, 1.0:

75 Moby Thesaurus words for "kowtow":
   apple-polish, bend, bend the knee, bend the neck, bend to,
   bending the knee, bob, bob a curtsy, bob down, bootlick, bow,
   bow and scrape, bow down, bow the head, bow to,
   bowing and scraping, brown-nose, butter up, cower, crawl, creep,
   cringe, cringe to, crouch, crouch before, curtsy,
   dance attendance on, dipping the colors, do homage, do obeisance,
   duck, fall down before, fawn, flatter, genuflect, genuflection,
   grovel, homage, inclination, kneel, kneel to, kneeling, knuckle to,
   lick the dust, lickspittle, make a leg, make a reverence,
   make obeisance, making a leg, nod, obeisance, obsequiousness,
   pander to, pay court to, play up to, presenting arms, prostration,
   reverence, salaam, salutation, salute, scrape, servility,
   shine up to, squat, standing at attention, stoop, submission,
   submissiveness, suck up to, supination, toadeat, toady, truckle,
   truckle to