The Collaborative International Dictionary of English v.0.48:

Tonsilitis \Ton`sil*i"tis\, n. [NL. See Tonsil, and -itis.]
   (Med.)
   Inflammation of the tonsils; quinsy. [Written also, and more
   usually, tonsillitis.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Tonsillitis \Ton`sil*li"tis\, n. (Med.)
   Inflammation of the tonsils; --- same as tonsilitis.
   [PJC]

WordNet (r) 3.0 (2006):

tonsillitis
    n 1: inflammation of the tonsils (especially the palatine
         tonsils)