Give both forms of the prefix meaning not, without, lacking, deficient.

The two forms of the prefix meaning "not, without, lacking, deficient" are "in-" and "un-".

1. "In-": This prefix is used with words of Latin origin. It can change its form to "il-", "im-", or "ir-" depending on the letter that follows in order to maintain phonetic harmony. Examples include "inaccurate", "illogical", "impossible", and "irregular".

2. "Un-": This prefix is used with words of Germanic (and by extension English) origin. Examples include "unhappy", "unfair", "unfit", and "unclear".