when

[ wen, hwen; unstressed wuhn, hwuhn ]

adverb

1. at what time or period? how long ago? how soon?:

   When are they to arrive?

   When did the Roman Empire exist?

2. under what circumstances? upon what occasion?:

   When is a letter of condolence in order?

   When did you ever see such a crowd?

conjunction

1. at what time:

   to know when to be silent.

2. at the time or in the event that:

   when we were young;

   when the noise stops.

3. at any time; whenever:

   He is impatient when he is kept waiting.

4. upon or after which; and then:

   We had just fallen asleep when the bell rang.

5. while on the contrary; considering that; whereas:

   Why are you here when you should be in school?

pronoun

1. what time:

   Till when is the store open?

2. which time:

   They left on Monday, since when we have heard nothing.

noun

1. the time of anything:

   the when and the where of an act.

when

/ wɛn /

adverb

1. 1. at what time? over what period?

      when is he due?

   2. ( used in indirect questions )

      ask him when he's due

2. say when
   to state when an action is to be stopped or begun, as when someone is pouring a drink
3. subordinating at a time at which; at the time at which; just as; after

   I found it easily when I started to look seriously

4. although

   he drives when he might walk

5. considering the fact that

   how did you pass the exam when you'd not worked for it?

6. at which (time); over which (period)

   an age when men were men

noun

1. usually plural a question as to the time of some occurrence

Usage

When should not be used loosely as a substitute for in which after a noun which does not refer to a period of time: paralysis is a condition in which (not when ) parts of the body cannot be moved

Word History and Origins

Origin of when¹

First recorded before 1000; Middle English when(ne), Old English hwenne; cognate with German wann “when,” wenn “if, when” (compare Gothic hwan “when, how”); akin to who, what

Word History and Origins

Origin of when¹

Old English hwanne, hwænne; related to Old High German hwanne, hwenne, Latin cum

Idioms and Phrases

• cross a bridge when one comes to it
• push comes to shove, when

Example Sentences

Notably, some of these compounds synergized -- that is, achieved "greater than the sum of its parts" latency reversal -- when administered with preexisting LRA compounds.

From Science Daily

"The reference genome was like a dictionary when we announced it," Ma said.

From Science Daily

These initiation sites contain regulatory elements and provide information to the cell about when and where to transcribe each gene to make protein, and how frequently to do so at any point in time.

From Science Daily

The Ohio-born comic further established his comedy cred when he became the youngest stand-up comedian to sell out the Hollywood Bowl during the second installment of the Netflix Is a Joke Festival in May.

From Los Angeles Times

Indeed, beyond the emotional heft of Smith’s music, it might be his background as a Nirvana- and Bush-obsessed child of the ’90s that’s helped him attract an audience at a moment when Nashville is in a serious rock phase.

From Los Angeles Times