The Collaborative International Dictionary of English v.0.48:

neck \neck\, v. i.
   To kiss and caress amorously. [Colloq.] -- n. necking.
   [PJC]

The Collaborative International Dictionary of English v.0.48:

Necking \Neck"ing\, n.
   Same as Neckmold.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Neck \Neck\, v. t. [imp. & p. p. Necked; p. pr. & vb. n.
   Necking.] (Mech.)
   To reduce the diameter of (an object) near its end, by making
   a groove around it; -- used with down; as, to neck down a
   shaft.
   [1913 Webster]

WordNet (r) 3.0 (2006):

necking
    n 1: the molding at the top of a column [syn: gorgerin,
         necking]
    2: affectionate play (or foreplay without contact with the
       genital organs) [syn: caressing, cuddling, fondling,
       hugging, kissing, necking, petting, smooching,
       snuggling]