what if

Short definition from Wiktionary

Adverb

1. 1
   Used to introduce a suggestion or proposal for a future event.
2. 2
   Used to introduce a speculation about a future event.
3. 3
   Used to introduce a speculation about a past event. Often the basis for counterfactual historical interpretations.

Noun

1. 1
   A speculation as to what might have happened if something else had happened earlier.
2. 2
   A hypothetical case or situation, usually evoked by a sense of anxiety or uncertainty.

Verb

1. 1
   To speculate about the consequences of something that could have happened.