Capital is not money, capital can be represented by money but it is not inherently money. Capital is something you use to buy someone’s labor. More specifically it is the social relationship between wage labor and profit. Assets (private property) used to produce profit (surplus value) are capital

Capital is “the characteristic the means of production acquire when they are used to hire labor and generate surplus value”

“Capital is dead labour, that, vampire-like, only lives by sucking living labour, and lives the more, the more labour it sucks.”