The Collaborative International Dictionary of English v.0.48:

Nag \Nag\, v. t. & i. [imp. & p. p. Nagged; p. pr. & vb. n.
   Nagging.] [Cf. Sw. nagga to nibble, peck, Dan. nage to
   gnaw, Icel. naga, gnaga, G. nagen, & E. gnaw.]
   To tease in a petty way; to scold habitually; to annoy; to
   fret pertinaciously. [Colloq.] "She never nagged." --J.
   Ingelow.
   [1913 Webster]