adv

• (interrogative) At what time? At which time? Upon which occasion or circumstance? Used to introduce direct or indirect questions about time.
  "When will they arrive?"
• (interrogative) At what time? At which time? Upon which occasion or circumstance? Used to introduce direct or indirect questions about time.
  "The site's all bugged. Fix when?"
• (relative) At which, on which, during which: often omitted or replaced with that.
  "That was the day when the Twin Towers fell."
• (fused relative) The time at, on or during which.
  "I recall when they were called the Greys."

pron

• (interrogative) What time; which time.
  "Since when do I need your permission?"

intj

• (often humorous) That's enough: a command asking someone to stop adding something, especially an ingredient or portion of food or drink; used in, or as if in, literal response to 'Say when'.
  "When we go out to a restaurant, we're the guys who never say "when" when the waiter is grinding fresh pepper on our salads."
• (obsolete) Expressing impatience.
  "Why when I ſay?[…]Off with my boots, you rogues: you villaines, when?[…]Out you rogue[…]"