calendar-month-name
calendar-month-name is a compiled Lisp function in `calendar.el
'.
(calendar-month-name MONTH &optional ABBREV)
Return a string with the name of month number MONTH.
Months are numbered from one. Month names are taken from the
variable `calendar-month-name-array', unless the optional
argument ABBREV is non-nil, in which case
`calendar-month-abbrev-array' is used.