rarely

As an adverb rarely is

not occurring at a regular interval; seldom; not often.

As adverbs the difference between rarely and sometime

is that rarely is not occurring at a regular interval; seldom; not often while sometime is at an unstated or indefinite time in the future.

As an adjective sometime is

former, erstwhile; at some previous time.

As an adverb rarely is

not occurring at a regular interval; seldom; not often.

As adverbs the difference between probably and rarely

is that probably is in all likelihood while rarely is not occurring at a regular interval; seldom; not often.

As adverbs the difference between occassionally and rarely

is that occassionally is while rarely is not occurring at a regular interval; seldom; not often.

As adverbs the difference between rarely and seldomly

is that rarely is not occurring at a regular interval; seldom; not often while seldomly is (rare|sometimes|proscribed) seldom; rarely.

As adverbs the difference between rarely and unoften

is that rarely is not occurring at a regular interval; seldom; not often while unoften is seldom, rarely.