IPA: /ʌnˈbɜːrnt/
KK: /ʌnˈbɜrnt/
Not damaged or destroyed by fire.
The unburnt wood was still usable for construction.
Unburnt → It is formed from the prefix "un-" (meaning not) and the root "burnt" (the past participle of "burn", which comes from Old English "byrnian", meaning to consume with fire). The word "unburnt" means not having been consumed by fire or not burned.
Think of 'not' ('un-') having been 'consumed by fire' ('burnt') — that's why unburnt means something that has not been burned.