Definitions

1. adverb

used to indicate the point or time at which something happens

“I’ll call you when I arrive at the airport.”

2. conjunction

used to indicate the time at which something happens

“I’ll be there when the movie starts.”

3. noun

a point in time

“I’m waiting for when my plane lands.”

4. preposition

used to indicate the time at which something happens

“I’ll see you when the clock strikes midnight.”