Polymorphic gates are capable of adapting to multiple functionalities depending on the application and need. In this paper, we propose a hybrid spin-CMOS polymorphic logic gate based on a novel 6 terminal composite magnetic domain wall motion device structure. As far as we know, we are the first to present a single polymorphic gate that is able to perform a full set of 2-input Boolean logic functions (i.e. AND/NAND, OR/NOR, NOT, XOR/XNOR) by configuring the applied keys. The SPICE device-circuit co-simulation indicates that a full adder design using our proposed polymorphic logic gate shows 45.74% power reduction compared with traditional CMOS full adder design. Moreover, it can be a promising hardware security primitive by implementing logic locking and polymorphic transformation to protect Integrated Circuit (IC) against counterfeiting and reverse engineering. To summarize, our proposed design simultaneously provides non-volatility, low power consumption, compactness and polymorphism to logic circuits, which opens a new paradigm for future power efficient and secured computing.