Adjective

(en adjective)

Not certain; unsure.

*(John Tillotson) (1630-1694)

*:Man, without the protection of a superior Being,is uncertain of everything that he hopes for.

Not known for certain; questionable.

:

Not yet determined; undecided.

Variable and subject to change.

Fitful or unsteady.

*

*:Turning back, then, toward the basement staircase, she began to grope her way through blinding darkness, but had taken only a few uncertain steps when, of a sudden, she stopped short and for a little stood like a stricken thing, quite motionless save that she quaked to her very marrow in the grasp of a great and enervating fear.

Unpredictable or capricious.

*Sir (Walter Scott) (1771-1832)

*:O woman! in our hours of ease, / Uncertain , coy, and hard to please!

Adjective

(en adjective)

Not secure.

Not comfortable or confident in oneself or in certain situations.

*{{quote-book, year=1963, author=(Margery Allingham)

, title=(The China Governess) , chapter=1 citation , passage=The half-dozen pieces […] were painted white and carved with festoons of flowers, birds and cupids. […]  The bed was the most extravagant piece.  Its graceful cane halftester rose high towards the cornice and was so festooned in carved white wood that the effect was positively insecure , as if the great couch were trimmed with icing sugar.}}

He's a nice guy and all, but seems to be rather insecure around other people.