E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898.
Specu’late
means to look out of a watch-tower, to spy about (Latin). Metaphorically, to look at a subject with the mind’s eye, to spy into it; in commerce, to purchase articles which your mind has speculated on, and has led you to expect will prove profitable. (Specula’ris lapis is what we should now call window-glass.)
