The assumption of risk in anticipation of gain but recognizing a higher than average possibility of loss. The term speculation implies that a business or investment risk can be analyzed and measured, and its distinction from the term Investment is one of degree of risk. It differs from gambling, which is based on random outcomes. There is nothing in the act of speculating or investing that suggests holding times, have anything to do with the difference in the degree of risk separating speculation from investing.
Speculation from 14c., "contemplation, consideration, contemplation, observation, to look at, view" (see scope). Disparaging sense of "mere conjecture" is recorded from 1570s. Meaning "buying and selling in search of profit from rise and fall of market value" is recorded from 1774. 
Investment 1590s, “act of putting on vestments, commercial sense is from 1610s, originally of the finances of the East India Company; general use is from 1740 in the general 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.” 
What is significant to note is the change from a passive to an active form of use. Specifically from a strict observer to one who contemplates what they observe then further to one who contemplates and acts on what they observe.
With these changes, the word as now commonly used, describes one who observes an object, event, or situation and takes some form of action with regard to the observed, all the while aware they may not know all the facts or factors regarding or affecting that which they observe. E.g. the financial speculator, one who understands and accepts he may not know all the facts or risks involved with a venture, yet chooses to invest his capital in the venture for the possibility of receiving greater capital in return.