Precarious, a.
Etymology: [L. precarius obtained by begging or prayer, depending on request or on the will of another, fr. precari to pray, beg. See Pray.]
1. Depending on the will or pleasure of another; held by courtesy; liable to be changed or lost at the pleasure of another; as, precarious privileges. Addison.
2. Held by a doubtful tenure; depending on unknown causes or events; exposed to constant risk; not to be depended on for certainty or stability; uncertain; as, a precarious state of health; precarious fortunes. "Intervals of partial and precarious liberty." Macaulay.
Syn. -- Uncertain; unsettled; unsteady; doubtful; dubious; equivocal. -- Precarious, Uncertain. Precarious in stronger than uncertain. Derived originally from the Latin precari, it first signified "granted to entreaty," and, hence, "wholly dependent on the will of another." Thus it came to express the highest species of uncertainty, and is applied to such things as depend wholly on future casualties. -- Pre*ca"ri*ous*ly, adv. -- Pre*ca"ri*ous*ness, n.
Shades of meaning
Uncertain is applied to things that human knowledge can not certainly determine or that human power can not certainly control; precarious originally meant dependent on the will of another, and now, by extension of meaning, dependent on chance or hazard, with manifest unfavorable possibility verging toward probability; as, one holds office by a precarious tenure, or land by a precarious title; the strong man's hold on life is uncertain, the invalid's is precarious.