*bheu-

The core idea of this root was:

being, existing, growing

The most famous English offspring is to be and the German forms bin and bist, but there are quite a few other interesting family members to be found.
Here’s an (incomplete) overview:

• physics, physical, … (“the existing, tangible world”)
• the beam (originally: “what’s existing, tree”)
• build (first “dwelling”, then “building a house”)
• neighbor (literally: “near-dweller”)
• husband (originally: “house dweller”)
• fiat (Latin for “be done”)
• future (Latin form for “going to be”)