When I checked up in the dictionary, they both have the meaning of "start" or "happen", or "come into effect"

If you get bitten by a dog, you have to make sure the wound is cleaned well, or an infection could set in.

Above is an example sentence from the Cambridge Dictionary. It basically means "an infection would happen"

An example sentence for "kick in" would be:

It takes half an hour for the medication to kick in.

It basically means the medication starts.

I don't quite get the subtle differences in meaning between the two words.

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  • Please give us example sentences for both phrases. I understand "kick in" but I'm not sure I understand what kind of usage you're thinking of for "set in" other than "set in motion." – KumaAra Oct 2 '17 at 2:36
  • As an intransitive verb, I would understand "kick in" to mean "become effective", when there is some delay after the cause of something "kicking in". E.g., after you take a drug, it takes ten minutes to "kick in". – Michael Hardy Oct 2 '17 at 2:38
  • 1
    The term "set in" is the phrasal verb "to set." It has connotations of something unpleasant happening – for example, "Bad weather had set in." – Livrecache Oct 2 '17 at 2:50
  • I agree with Livrecache - compare then the depression set in with then the annuities kicked in. – Davo Oct 2 '17 at 14:41

The phrase "kick in" is usually used in context of something being activated in a short amount of time. Generally, it is also used when there is a period of time when there is no effect from the thing that "kicks in."

For example, let's look at "I'm waiting for the medicine to kick in."

  1. Notice that there is a period of inactivity between taking the medicine and the medicine's effect.
  2. The use of "kick in" implies that once the medicine begins affecting the body, its effects will be quick to materialize.

"Set in," on the other hand, is used for gradual motion/effect (rather than sudden), motion/effects that last a long time, and tends to be used in a less desirable context. (It's also most commonly used to describe undesirable weather).

As an example, look at: "We knew we were in it for the long haul when the snowstorm set in."

  1. Notice how "set in" in combination "long haul" makes the situation seem less than desirable.
  2. Using "set in" sets up an image in the reader's head of a slow-moving mass of clouds that moves towards the speaker, and, once it reaches the speaker, lets loose a snowstorm that lasts for several days.

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