-ly

Some adverbs are composed of the suffix -ly added to an adjective, or, more rarely, a word from some other class.

Note that the suffix contains a single '-l-'. When such an adverb ends with '-lly' (a double '-l-' followed by '-y'), it is because the parent adjective itself ends in '-l', so that the whole adverb contains the final letter of the adjective plus a second '-l-' from the suffix.