"Mutt" etymology (speculative)

[Douglas G. Wilson]

>Question:  Doesn't "mutt" always refer to a "mixed-breed" dog?

Often, but not always. It can refer to any dog in a disparaging or humorous
way, I believe.

I have a copy of the "Century Dictionary", apparently printed in the 1930's
(but maybe not revised in timely fashion), which does not even include the
"mongrel" sense, so maybe the "mongrel" sense has become more prevalent
over the course of the last century. My OED and RHUD say "especially a
mongrel" or words to that effect. MW3 seems to say that "mutt" = "mongrel".

Since "mutt" is basically derogatory/deprecatory, it would never have been
used often for a dog known to have a registered pedigree, I suppose, except
in humor or anger or so ... but I think it has generally been applied
freely to dogs of unknown ancestry (who may or may not be pure-bred).

-- Doug Wilson