械 is a bound form (b.f.) that only appears as part of multi-syllable words — never alone. It has two broad semantic clusters: (1) machinery or mechanical devices, as in 机械 (machinery) and 器械 (apparatus/equipment), and (2) weapons or instruments of violence, as in 枪械 (firearms) and 械斗 (armed conflict). When you encounter 械 in a compound, context tells you which sense is active.