1. Open something sealed, make a breakthrough
crack open a window
The phrasal verb to 'crack open' can mean to open something which is sealed, such as to 'crack open a bottle' of something alcoholic, or to 'crack open a can'. To 'crack open' something can also mean to open or unlock something so you can 'crack open' a door or a window'. To crack open something can also mean to expose or reveal something.