Both words refer to setting something going or putting it in motion. Start has a wider range of usage. We can say someone starts a car, starts a club, or starts an argument. Instigate, which derives from a Latin root meaning “to prick” or “to goad,” refers to prompting a human activity by urging or spurring it on. The object of instigate is usually an act of aggression or hostility (instigated a riot; instigated a war), so the word tends to have a negative connotation. However, instigating change is one common and more positive use, and both instigating a project and instigating a discussion are also fairly common and less negative.

Both words refer to arriving at the final point or stage of something. When a movie ends, it’s over. The sense of end we’re concerned with here can stand alone, as in the example above, or it can be followed by a prepositional phrase stating how something ended: The scene ends with a fade-out. Culminate works as a strong synonym for end in cases like this because it’s normally followed by the preposition “in,” or sometimes “with.” Culminating with a fade-out could be a bit self-contradictory, however, because culminate, which comes from a Latin word for “top” or “peak,” suggests ending at a high, ultimate, or conclusive point: This nail-biting scene culminates in a shocking revelation.

Both words refer to someone or something that poses a danger to us. A threat in this sense is not the verbal warning (Is that a threat?), but something that jeopardizes, or could jeopardize, life, peace, health, or other desirable conditions currently intact: a threat to national security. Menace can be a strong synonym for threat, when the harm is imminent or even already occurring, as with the menace of crime, corruption, pollution, and stray dogs.The difference in meaning can be seen in the verbs that typically precede each word. We want to eliminate a threat before the harm comes to pass, but a menace already has a troubling presence we tackle, curb, deal with, or eradicate. Gang culture is a threat to the community, whereas the presence of gangs has become or is a menace.