IPA: /ˈsændbɒks/
KK: /ˈsændbɑks/
A container filled with sand where children can play, often found in playgrounds.
The children had a great time building castles in the sandbox.
Sandbox → The word is formed from "sand" (from Old English "sand", meaning granular material) and "box" (from Old English "box", meaning a container). A sandbox is essentially a container filled with sand, typically for children to play in.
Think of a 'container' ('box') filled with 'granular material' ('sand') — that's what a sandbox is.