Depending on what version OS X your MacBook has installed, and what MacBook you have this could vary, there are several Safari browser versions. Some are available for download via the Mac App store if your computer is running OS X 10.6.8 or Later...
•Apple - Support - Mac Apps - Safari:
There are links to look into downloading certain older Safari versions in the above page.
Is only the icon in the Dock missing, or is the application gone from the Applications folder? If there is one in the Applications folder, just drag it into the Dock to restore an icon access there.
Hopefully this helps.
Good luck & happy computing!