IPA: /ˌɪnɪkˈspleɪnəbl/
KK: /ɪnɪkˈspleɪnəbl/
Something that is difficult or impossible to explain or understand.
The sudden change in his behavior was completely inexplainable to his friends.
Inexplainable → It is formed from "in-" (meaning not) and "explain" (from Latin "explanare", meaning to make clear or to unfold) and "-able" (meaning capable of). The word "inexplainable" means not capable of being made clear or understood.
Think of 'not' ('in-') being added to 'explain' — this helps you remember that 'inexplainable' refers to something that cannot be made clear.