An arch is a curve that spans an opening, and a bow is half of an arch.
In an architectural context, an Arch can bear a lot of weight by directing force down to the base of the arch.
A Bow is half of an arch — so you can use two of them to create a full arch or use just one for branches of a tree or other curved creations.
 | 1×3 Arch 4490 |
 | 1×4 Arch 3659 |
 | 1×4×2 Arch 6182 |
 | 1×6 Arch 92950 |
 | 1×6×2 Arch 15254 |
 | 1×8×2 Arch 16577 |
 | 1×12×3 Arch 18838 |
 | 1×2 Dbl. ½-Arch 38583 |
 | 1½×1½×1 Dbl. ½-Arch 38585 |
 | 8×1 Curved w/ Arch 50967 |
 | 1×3×2 Bow, Pointed 88292 |
 | 1×3×3 Bow, Pointed 13965 |
 | 1×4×3 Bow 80543 N |
 | 1×5×4 Bow 14395 |
 | 1×5×2 Bow 3572 N |
 | 1×5×4 Bow, Inverted 30099 |
 | 1×3×2 Bow, Inverted 18653 |
 | 1×4×6 Arch w/ Pillars 40066 |
 | 3×6×5 Arch, Ornamented 30613 |