B1
to close or attach something together, or to become closed or attached together
Dictionary examples:
He fastened his tie so quickly, it looked like a magic trick. (0.0)
I tried to fasten my pants, but the burger won. (0.0)
The boy fastened his teddy bear to his backpack for protection. (0.0)
This shirt fastens at the back. (21.4)
Fasten your seat belt. (37.4)