Why is the ninth month called September?
1590s, "act of putting on vestments" (a sense now found in investiture); later "act of being invested with an office, right, endowment, etc." (1640s); and "surrounding and besieging of a military target" (1811); see invest + -ment. Commercial sense is from 1610s, originally of the finances of the East India Company; general use is from 1740 in the sense of "conversion of money to property in hopes of profit," and by 1837 in the sense "amount of money so invested; property viewed as a vehicle for profit." For evolution of commercial senses, see invest.
The purchase of property with the expectation that its value will increase over time.