Whilst several not-very-authoritative sources e.g. Wikipedia state that the word qubit was derived, partially, as a play on the word cubit (obviously it also stands for 'quantum bit'), is there any credible source for this?
The coining of the term "qubit" is attributed to Benjamin Schumacher. In the acknowledgments of his paper, Schumacher states that the term qubit was invented in jest due to its phonological resemblance with an ancient unit of length called cubit, during a conversation with William Wootters.
However, Schumacher (1995) (the above referenced paper) merely states:
The term "qubit" was coined in jest during one of the author's many intriguing and valuable conversations with W. K. Wootters, and became the initial impetus for this work.
'In jest' would suggest it's perhaps not merely derived from 'quantum bit', but there's no further information. In fact the only source I can find that mentions qubit and cubit together in this context is Mermin (2007, p. 4) (whom I don't have the reputation to hyperlink but DOI: 10.1017/CBO9780511813870):
My guess is that “qubit” has gained acceptance because it visually resembles an obsolete English unit of distance, the homonymic cubit.
Which really doesn't tell us anything.