Prescribe and proscribe -- keep them straight, keep them separate. Oddly enough, both mean (more or less) "enjoin," but let's not go there.
Flammable is an oddity, chiefly useful in saving lives. The common word meaning "combustible" is "inflammable." But some people are thrown off by the "in-" and think "inflammable" means "not combustible." For this reason, trucks carrying gasoline or explosives are marked "flammable." Unless you are operating such a truck and hence are concerned with the safety of children and illiterates, use "inflammable."
Here's another -- the UCC spells the word, " indorse", but in every other context, I have only seen it spelled, "endorse."