Capable of being commuted.
Able to be exchanged, one for the other, especially
Able to be exchanged for foreign currency.
Able to be exchanged for a different class of security (usually common stock) under certain set terms.
Able to be turned to a different purpose.
Able to be turned to a different religion or belief.
Able to undergo conversion (i.e., inversion) without falsehood.
Able to change from a closed to an open frame and back again.
Able to be exchanged for specie.
A convertible security: a stock, bond, etc. that can be turned into another (usually common stock) under certain set terms.
A convertible car: a car with a removable or foldable roof able to convert from a closed to open vehicle and back again.
A computer able to convert from laptop to tablet and back again.