IPA: /ˈsmoʊkˌboʊks/
KK: /ˈsmoʊkˌboʊks/
A chamber where smoke goes after leaving a boiler and before it exits through a chimney.
The engineer checked the smokebox to ensure it was clear of any blockages.
Smokebox is formed from "smoke" (from Old English *smoca*, meaning vapor or fume) and "box" (from Old English *box*, meaning a container). The word "smokebox" refers to a container designed to hold or produce smoke.
Think of a 'container' ('box') that holds 'vapor' or 'fume' ('smoke') — that's what a smokebox is.
No commonly confused words.