'Of a sudden' definitions:

Definition of 'of a sudden'

From: WordNet
adverb
Happening unexpectedly; "suddenly she felt a sharp pain in her side" [syn: suddenly, all of a sudden, of a sudden]

Definition of 'Of a sudden'

From: GCIDE
  • Sudden \Sud"den\, n. An unexpected occurrence; a surprise. [1913 Webster]
  • All of a sudden, On a sudden, Of a sudden, sooner than was expected; without the usual preparation; suddenly. [1913 Webster]
  • How art thou lost! how on a sudden lost! --Milton. [1913 Webster]
  • He withdrew his opposition all of a sudden. --Thackeray. [1913 Webster]