The quickest way to flip a word into its opposite is to put “not” in front. English has three prefixes for that. un- is the old English one (unkind, unhappy). in- came with Latin words (invisible, incredible). non- is plain and blunt (nonstop, nonfiction).
Key idea
un-, in- and non- all mean not. in- changes shape to fit the next sound: im- before b, m and p (impossible, immutable), il- before l (illegal) and ir- before r (irregular, irrevocable).
Many of the strongest words on the list are “not” words. Most of them pair in- with the ending -able or -ible, giving the pattern “not able to be ___”: indelible (not able to be wiped out), insatiable (not able to be filled), irrevocable (not able to be called back).
The parts and their words
Words taken apart
| Word and meaning | Parts, and what they say |
|---|---|
| impeccable without any flaw or fault | im- not + pecc to sin, to err + -able able to → “not able to do wrong” |
| indelible impossible to remove or forget | in- not + del wipe out + -ible able to be → “not able to be wiped out” |
| immutable unchanging | im- not + mut change + -able able to be → “not able to be changed” |
| insatiable impossible to satisfy | in- not + sati enough, full + -able able to be → “not able to be filled up” |
| irrevocable impossible to undo or take back | ir- not + re- back + voc call + -able able to be → “not able to be called back” |
| impartial treating all sides equally | im- not + partial taking one part → “not taking sides” |
| unprecedented never done or known before | un- not + pre- before + ced go + -ent + -ed → “with nothing gone before it” |
| nonchalant casually calm and unconcerned | non- not + chal be concerned (old French) + -ant → “not concerned” |
Worked example: Use the parts
The coach’s decision was inexorable: no begging changed it. What does inexorable mean?
- Take it apart: in- (not) + ex- (out) + or (plead, pray, as in orator) + -able (able to be).
- Put it together: “not able to be pleaded out of.”
- The sentence agrees: no begging changed the decision.
Answer: Impossible to stop or change.
Meet the words
Common mistake
Reading every in- as “not.” A different prefix in- means “in” or “into”: inhale (breathe in), incite (stir into action), inundate (flood into). The trickiest case is inflammable: it means easily set on fire, the same as flammable, because its in- means “into” (into flame). Signs say flammable for exactly this reason.
To tell the two in-s apart, try “not”: incredible = not believable works, so its in- means not. Inhale = “not hale” makes no sense, so its in- means into.