There is some dictionary support for the term "nob" as British slang that means either "head" or a "wealthy and important person". EtymOnline gives only one history of the term, and says it means:
"head," c.1700, variant of knob (q.v.).
Wiktionary suggests some other etymologies, both of which highlight that the term refers to someone of high rank:
- From "nobleman" or "member of the nobility" (Doubtful)
- From "white-nob" (Eighteenth century) or "white-head", referring to the powdered wigs used by those affecting upper middle-class status.
Wiktionary also lists possible definitions of "nob" that include (besides a slang term for genitalia):
- (slang) the head (somewhat archaic): Used in one version of the Nursery Rhyme: Jack and Jill went up the hill to fetch a pail of water; Jack fell down and broke his crown, and Jill came tumbling after. Up Jack got and home did trot, as fast as he could caper; to old Dame Dob to mend his nob, with vinegar and brown paper.
Since there is no one definition, it is possible that the meanings are related. For example, "head" is a literal place that is "higher up", and someone who is important is figuratively "higher up". Despite the multiple definitions, one cribbage site gave some history, mentioning that "nob" is the "term for noble or superior person".
Depending on the definition used, the term is either from around the late 16th to early 17th century. Since cribbage was invented around this time, "nob" could refer to either one of these meanings.
Whichever meaning it refers to, either the figurative or literal definition of "nob" meaning head or important, the rules of cribbage build upon the notion of importance:
The nob Jack (or "right Jack" as it's also known), is essential for scoring a perfect 29 hand, and also affects discard strategy - you should try to avoid throwing a Jack to your opponent's crib if possible.
So the "nob Jack" is a strategically important card, and its name possibly derives from this.
Nib: @Kit mentioned that some people refer to "his nibs" or "nib" instead of "nob". This is another somewhat accepted term that has similar origins. There is, however, some debate about which is correct:
Throughout Cribbage history, the term “nibs” and “nobs” (or “his nibs” and “his nobs”) have been interchangeable. However, with the rise of Cribbage Inc., and its lesser president Robert A. “Nibsmonger” Laird, many serious cribbers among us have begun to research which one is the correct one. Although most have reasoned that “nobs” is the correct term, many (most notably the “Nibsmonger” himself!), refuse to yield “nibs”. Many a cribber has argued in vain to come up with a solution, and the debate rages on to this day, and probably will until the end of time.
Whichever term is "historically accurate", nib has a similar meaning as the slang nob. Wiktionary says that one definition is:
(slang, UK) An important or self-important person.
This is slightly different from the aforementioned definition of "nob", but it still seems to refer to someone who believes he is (or is) important. The term "his nibs" has entered into the vocabulary of some, which lead one person to ask for its origins:
This is a mock title used to refer to a self-important man, especially one in authority.... Also, nib itself was once used as a slang term for a gentleman, as was another old slang word still to be heard, nob, and these could very probably be connected. Several early examples of the latter are spelled nab and his nabs is a variant recorded form of his nibs. It seems the vowel was highly fluid, not surprising considering the different dialects and periods it has come through.
The last point brought up in this article may point to the reason there is a "nib/nob" debate--vowels have come to be pronounced differently over time.