A subordinating conjunction used to introduce conditional clauses.
It can also be used:
 With what to form questions about things that might happen in the future or might have happened in the past:
What if I find certain issues or situations difficult?
What if he had become much more ruthless in that time?
 To modify an adjective or adverb:
It was a delicious, if small, compensation.
Trade unions began, if slowly and unadventurously, to assert that they didn’t give a hoot.
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