Definition of uncertain :
1. Irresolute; inconsonant; variable; untrustworthy; as, an uncertain person; an uncertain breeze.
2. Not certain; not having certain knowledge; not assured in mind; distrustful.
3. Not sure; liable to fall or err; fallible.
4. Questionable; equivocal; indefinite; problematical.
5. To make uncertain.
whimsical, changeful, mistrustful, inexplicit, private, personal, suppositious, up in the air, short-lived, nebulous, shady, chatoyant, various, suppositional, inclined to think/believe/agree etc., fluid, flickery, conjectural, enigmatic, suspect, borderline, improbable, fleeting, fluctuating, fantastic, brief, undetermined, chancy, unreliable, certain, enigmatical, continue, contested, short-term, mutable, shot, hypothetical, anonymous, obscure, exceptionable, dubitable, distrustful, unsure of yourself, mootable, honest, sceptical, unlikely, change, doubtful, problematic, hinky, dubious, ill at ease, ticklish, incertain, temporary, trustless, inconstant, clear, fishy, lost, theoretical, transient, unsettled, unsafe, open, bewildered, hidden, unclear, indeterminate, flukey, retiring, variable, iridescent, diffident, questioning, unsteady, strange, inhibited, temperamental, suspicious, alterable, cloudy, mercurial, fantastical, iffy, timid, unstable, unknown, provisional, skittish, freakish, unpredictable, passing, problematical, secret, unsealed, variant, indistinct, casual, groping, clouded, possible, indefinite, floating, perplexing, contingent
circumstantial (part of speech: adjective)
disbelieving (part of speech: adjective)
chancy (part of speech: adjective)
equivocal (part of speech: adjective)
uncertain (part of speech: adjective)
irresolute (part of speech: adjective)
inconsistent, unresolved, halfhearted, dillydallying, shrinking, capricious, indecisive, undecided, unsure, infirm, tentative, vacillating, irresponsible, insipid, shy, fickle, irresolute, shifty, yellow, unwilling, changeable, impulsive, double-minded, shilly-shally, undependable, watery, fly-by-night, erratic, weak, volatile, hesitant, spineless, flitting
- He may do so, m'sieur; but his plans are uncertain. - "The Sins of Séverac Bablon", Sax Rohmer.
- The day had been uncertain. - "The White Peacock", D. H. (David Herbert) Lawrence.
- But it seemed to Laurence Stanninghame that a warning note had been sounded, and one of no uncertain nature. - "The Sign of the Spider", Bertram Mitford.