家伙 (jiā huo) is a colloquial noun with two main uses: it can mean 'guy, fellow' (often with a familiar or teasing tone) or 'thing, tool, weapon' (informal). For the 'guy' sense, 男生 (nán shēng) is more neutral and specific to young men; 家伙 is broader and more casual. For the 'weapon' sense, 武器 (wǔ qì) is the standard term, while 器械 (qì xiè) is formal equipment; 家伙 is only used in everyday speech.