You never mean: preventative You always mean: preventive Why: Grammar sovereign H. W. Fowler banned the long form almost a hundred years ago. So someone who is health conscious might seek preventive care; responsible homeowners might take preventive measures to keep their roof from leaking.
You almost never mean: infamous You almost always mean: famous Why: The rich and famous are widely known (and wealthy). But the rich and infamous have a reputation of the worst kind (… and money, which doubtless has dubious origins). Another way to look at it: Unless Aunt Donna’s chocolate chip cookies are notoriously evil and disgraceful, they are famous, not infamous.
You might say: evoke You might mean: invoke Why: A photograph evokes emotion; a joke evokes laughter—evoke means “to elicit or call forth.” Save invoke for when you mean “to call on a higher power, petition for support, or implement” (for example, “Allison invoked Robert Frost for her first assignment” or “The principal invoked the aid of the teachers”).
You might say: denounce You might mean: renounce Why: The two may sound similar, but their meanings are distinct: Denounce is “to condemn publicly or accuse formally” (“The judge denounced the CEO for insider trading”), while renounce means “to give up or refuse to follow” (“The CEO renounced his not-guilty plea”).
You might say: uninterested You might mean: disinterested Why: Careful speakers who wish to convey a lack of bias want to use disinterested. Speakers who don’t care about such grammatical subtleties are uninterested.