un- (adjectives) not (ex. unfair; unfairly; unfairness; unfelt; unseen; unfitting; unformed; unheard-of; un-get-at-able)

      (verbs) reversal of some action (ex. unbend; uncork; unfasten)

sub-  “under,” “below,” “beneath” (subalpine; substratum), “slightly,” “imperfectly,” “nearly” (subcolumnar; subtropical), “secondary,” “subordinate” (subcommittee; subplot)

mid- middle (ex. midday, midpoint, midfield)

re- “again” or “again and again” to indicate repetition, or with the meaning “back” or “backward” to indicate withdrawal or backward motion: regenerate; refurbish; retype; retrace; revert

dis- a Latin prefix meaning “apart,” “asunder,” “away,” “utterly,” or having a privative, negative, or reversing force (see de-, un-²); used freely, esp. with these latter senses, as an English formative: disability; disaffirm; disbar; disbelief; discontent; dishearten; dislike; disown.

non- a prefix meaning “not,” freely used as an English formative, usually with a simple negative force as implying mere negation or absence of something (rather than the opposite or reverse of it, as often expressed by un-¹): nonadherence; noninterference; nonpayment; nonprofessional.

over- a prefixal use of over, preposition, adverb, or adjective, occurring in various senses in compounds (overboard; overcoat; overhang; overlap; overlord; overrun; overthrow), and especially employed, with the sense of “over the limit,” “to excess,” “too much,” “too,” to form verbs, adjectives, adverbs, and nouns (overact; overcapitalize; overcrowd; overfull; overmuch; oversupply; overweight), and many others, mostly self-explanatory: a hyphen, which is commonly absent from old or well-established formations, is sometimes used in new coinages or in any words whose component parts it may be desirable to set off distinctly.

pre- a prefix occurring originally in loanwords from Latin, where it meant “before” (preclude; prevent); applied freely as a prefix, with the meanings “prior to,” “in advance of,” “early,” “beforehand,” “before,” “in front of,” and with other figurative meanings (preschool; prewar; prepay: preoral; prefrontal).

im-var. of in-² before b, m, p: imbrute; immigrate; impassion.

in- a prefix of Latin origin, corresponding to English un-, having a negative or privative force, freely used as an English formative, esp. of adjectives and their derivatives and of nouns (inattention; indefensible; inexpensive; inorganic; invariable). It assumes the same phonetic phases as in- ² (impartial; immeasurable; illiterate; irregular, etc.). In French, it became en- and thus occurs unfelt in such words as enemy (French ennemi, Latin inimicus, lit., not friendly).