IPA: /ˈstɒpəbl/
KK: /ˈstɑpəbl/
Able to be stopped or prevented from continuing.
The runaway train was finally stopped by a quick-thinking engineer.
Comparative: more stoppable
Superlative: most stoppable
Stoppable is formed from "stop" (from Old English "stoppian", meaning to close or block) and "-able" (meaning capable of). The word "stoppable" means capable of being stopped.
Think of something that can be 'closed' or 'blocked' ('stop') and is 'capable of' ('-able') being halted.