What word means the opposite of often?

The opposite of "often" depends on the context. Here are some possibilities:

If you mean "rarely":

* Seldom

* Rarely

* Infrequently

* Occasionally

* Scarcely

If you mean "never":

* Never

* Not at all

If you mean "sometimes":

* Sometimes

* Occasionally

If you mean "not habitually":

* Unusually

* Exceptionally

* Invariably

Example:

* "He often forgets his keys."

* "He rarely forgets his keys."

The best word to use depends on the specific meaning you want to convey.