of beef. Corruption of “Naitch-bone,” i.e. the haunch-bone (Latin, nates, a haunch or buttock).
Similarly, “an apron” is a corruption of a napperon; “an adder” is a corruption of a nadder (Old Eng., næddre). In other words, we have reversed the order; thus “a newt” is an ewt , “a nag” is an ög (Danish). Latin, eq[uus], a horse.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894