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:

Hickup \Hick"up\, n. & v. i.
   See Hiccough. Hickwall