The Collaborative International Dictionary of English v.0.48:

Flagellation \Flag`el*la"tion\, n. [L. flagellatio: cf. F.
   flagellation.]
   A beating or flogging; a whipping; a scourging. --Garth.
   [1913 Webster]

WordNet (r) 3.0 (2006):

flagellation
    n 1: beating as a source of erotic or religious stimulation
    2: beating with a whip or strap or rope as a form of punishment
       [syn: whipping, tanning, flogging, lashing,
       flagellation]

Moby Thesaurus II by Grady Ward, 1.0:

67 Moby Thesaurus words for "flagellation":
   Albigensianism, Catharism, Day of Atonement, Franciscanism,
   Sabbatarianism, Trappism, Waldensianism, Yoga, Yom Kippur,
   abstinence, anchoritic monasticism, anchoritism, asceticism,
   austerity, bastinado, basting, battery, beating, belting,
   buffeting, caning, clubbing, cold purgatorial fires,
   corporal punishment, cowhiding, cudgeling, drubbing, eremitism,
   fasting, flailing, flogging, fustigation, hair shirt,
   horsewhipping, lacing, lashing, lustration, maceration,
   mendicantism, monachism, monasticism, mortification, penance,
   penitence, penitential act, penitential exercise, pistol-whipping,
   purgation, purgatory, puritanism, rawhiding, repentance, rigor,
   sackcloth and ashes, scourging, self-denial, self-mortification,
   spanking, strapping, stripes, swingeing, switching, thrashing,
   trouncing, truncheoning, voluntary poverty, whipping