safari browser

Have you checked your Applications folder?

Do a backup, preferable 2 separate ones on 2 drives. Boot to the Recovery Volume (command - R on a restart). Run Disk Utility and select First Aid. Then re-install the OS.

Reinstall from macOS Recovery

OS X Recovery

OS X Recovery (2)

Others have asked this when they’ve inadvertently removed the Safari icon from the toolbar. In that case, follow Eric’s first suggestion and, after Safari is open, control-click on the icon in the dock, selecting Options then Keep in Dock.