'Speculation' is Latin for 'watching from a vantage' — the financial sense of risk arrived in the 1700s.
The forming of a theory or conjecture without firm evidence; investment in stocks, property, or other ventures in the hope of gain but with the risk of loss.
From Latin 'speculātiō, speculātiōnis' (contemplation, observation, spying), from 'speculārī' (to observe, to watch, to spy out), from 'specula' (watchtower), from 'specere' (to look at, to see). The financial sense developed in the eighteenth century: a speculator 'watches' the market from a vantage point and bets on what they see coming. The same root gave English
The words 'speculation,' 'spy,' and 'spectacle' all come from PIE *speḱ- (to look). A speculator is etymologically someone looking out from a watchtower; a spy is someone looking secretly; a spectacle is something worth looking at. Even 'species' (a type of thing) is from the same root: a species is defined by how it 'looks' — its appearance.