Answer:
"able" comes from the Latin word "habilis" which also means able, or capable. "Habilis" comes from the Latin verb "habere", to have/hold, and the suffix "ilis", equivalent to the English suffix "ile" (denoting capability).
As Latin evolved into other languages such as Spanish throughout the ages, the "h" sounds became silent, which is why we now have "able" and not "hable"!