Webster’s Revised Unabridged Dictionary · 1913
Conjecture
Con·jec′ture, n. [L. conjectura, fr. conjicere, conjectum, to throw together, infer, conjecture; con- + jacere to throw: cf. F. conjecturer. See Jet a shooting forth.] An opinion, or judgment, formed on defective or presumptive evidence; probable inference; surmise; guess; suspicion.
He [Herodotus] would thus have corrected his first loose conjecture by a real study of nature. Whewell.
Conjectures, fancies, built on nothing firm. Milton.
Con·jec′ture, v. t. [imp. & p. p. Conjectured; p. pr. & vb. n. Conjecturing.] [Cf. F. conjecturer. Cf. Conject.] To arrive at by conjecture; to infer on slight evidence; to surmise; to guess; to form, at random, opinions concerning.
Human reason can then, at the best, but conjecture what will be. South.
Con·jec′ture, v. i. To make conjectures; to surmise; to guess; to infer; to form an opinion; to imagine.