We don't have synonyms for xember yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are member, ember and rember.
(n) :
(obsolete) Alternative spelling of December. [The twelfth and last month of the Gregorian calendar, following November and preceding the January of the following year, containing the southern solstice.]
(n) :
(obsolete) Alternative spelling of December. [The twelfth and last month of the Gregorian calendar, following November and preceding the January of the following year, containing the southern solstice.]