We received a request on the blog for information on the name Jolyon. This is a curious name, because two of the main authorities on English onomastics, E.G. Withycombe and P.H. Reaney & R.M. Wilson disagree as its etymology!
Withycombe, s.n. Julian makes it a derivative of Julian, the name of 10 medieval saints and used in England from the 13th C on. (It was never as popular there as its feminine counterpart, Juliana.) Reaney & Wilson, on the other hand, identify it (s.n. Jolyon) as a byname, ‘jolly Jan’. They have examples of similar constructions s.n. Jollyboy, including Jolifion 1377 ‘jolly Ion (John)’ and Jolyrobin 1332 ‘jolly Robin’.
The answer is probably a compromise: Both origins are plausible, and the only way to tell for sure would be to find a record referring to the same person as both Julian and Jolyon. We haven’t found any yet, but if we do, we’ll update this post!