when

[hwen, wen, hwuhn, wuhn]

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. 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

When the asteroid data is plotted on a graph of the rotation period versus diameter, something startling stands out - there's a gap, or dividing line that appears to split two distinct populations.

From Science Daily

"When these two effects balance, they create a natural dividing line in the asteroid population."

From Science Daily

Tumbling motion usually starts when an asteroid spins slowly.

From Science Daily

When the loop currents inside these metals change direction, the electrical behavior of the metal changes.

From Science Daily

When scientists apply weak magnetic fields, they reverse the direction these currents spin, and as a result, the preferred direction of current flow in the metal changes.

From Science Daily