OK, this is one i had to look up.

i still have trouble with calendar and calender.
One is from the latin, (calends) for the first day of the month, the other from the greek, kylindein, (to roll) -which also gives use cylinder.
(to calender paper it to roll (between heavy rollers) to make it smooth and glossy.

Calendar's (especially one with pretty pictures,) are often printed on calender paper.
(i know, not on topic...)


my other obsession