The present work provides a straightforward two-step strategy of carbonization, followed by KOH activation, for transforming Borassus flabellifer fruit flesh, one of the cost-effective and sustainable lignocellulose biomass to porous activated carbon for utilization in energy storage systems. The acquired activated Borassus flabellifer fruit flesh (ABFF) carbon exhibits features like high surface area (∼1087.8 m2 g-1) with surface functionalities, hierarchical porous morphology (presence of micropores and mesopores), together with some partially graphitic domain, some of the prerequisites for demonstration of excellent electrochemical performance. Taking advantage of the structural features and chemical composition, the ABFF carbon, when assembled in a symmetrical two-electrode configuration, exhibits an impressive specific capacitance of 226 F g-1 and 159 F g-1 in 1 M H2SO4 and neat ionic liquid (IL) EMIMBF4 electrolyte. The as-fabricated symmetric device attained a maximum energy density of 8 Wh kg-1 in the aqueous medium, while an enhanced energy density of 50 Wh kg-1 was achieved in the nonaqueous medium. ©