un ‧ zip /ʌnˈzɪp/ BrE AmE verb ( past tense and past participle unzipped , present participle unzipping ) [transitive]
1 . to unfasten the ↑ zip on a bag, piece of clothing etc
2 . to make a computer ↑ file its normal size again so that you can use it, after it has been made to use less space