hadn't
uk/ˈhæd.ənt/us/ˈhæd.ənt/short form of had not:
If you hadn't told him he would never have known.
More examples
- She was disappointed that they hadn't phoned.
- Four years after he left college he still hadn't found a job.
- The examiners failed him because he hadn't answered enough questions.
- She looked as though she hadn't slept all night.
- I'd have drowned if he hadn't been there to pull me out of the river.