The Collaborative International Dictionary of English v.0.48:

Nad \Nad\ (n[a^]d), Nadde \Nad"de\ (n[a^]d"de). [Contr. fr. ne
   hadde.]
   Had not. [Obs.] --Chaucer.
   [1913 Webster]

WordNet (r) 3.0 (2006):

NAD
    n 1: a coenzyme present in most living cells and derived from
         the B vitamin nicotinic acid; serves as a reductant in
         various metabolic processes [syn: nicotinamide adenine
         dinucleotide, NAD]