The Collaborative International Dictionary of English v.0.48:

Hiccough \Hic"cough\ (?; 277), n. [OE. hickup, hicket, hickock;
   prob. of imitative origin; cf. D. & Dan. hik, Sw. hicka,
   Armor. hak, hik, W. ig, F. hoquet.] (Physiol.)
   A modified respiratory movement; a spasmodic inspiration,
   consisting of a sudden contraction of the diaphragm,
   accompanied with closure of the glottis, so that further
   entrance of air is prevented, while the impulse of the column
   of air entering and striking upon the closed glottis produces
   a sound, or hiccough. [Written also hickup or hiccup.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Hiccough \Hic"cough\, v. i. [imp. & p. p. Hiccoughed; p. pr. &
   vb. n. Hiccoughing.]
   To have a hiccough or hiccoughs.
   [1913 Webster]

WordNet (r) 3.0 (2006):

hiccough
    n 1: (usually plural) the state of having reflex spasms of the
         diaphragm accompanied by a rapid closure of the glottis
         producing an audible sound; sometimes a symptom of
         indigestion; "how do you cure the hiccups?" [syn: hiccup,
         hiccough, singultus]
    v 1: breathe spasmodically, and make a sound; "When you have to
         hiccup, drink a glass of cold water" [syn: hiccup,
         hiccough]