Based on Bill Verners' Inside the Java Virtual Machine, McGraw Hill Companies, 1997

ret - Return from subroutine

opcode:  169 (0xa9)   usage: ret index   stack: No change.   description: Returns to the address held in local variable index.

return - Return (void) from method

opcode:  177 (0xb1)   usage: return   stack before: ... stack after: [empty]   description: Leaves the method of return type void.