adj. 25B6; adjective
an insecure young man : UNCONFIDENT, uncertain, unsure, doubtful, hesitant, self-conscious, unassertive, diffident, unforthcoming, shy, timid, retiring, timorous, inhibited, introverted; anxious, fearful, worried; informal mousy.
insecure windows : UNGUARDED, unprotected, vulnerable, defenceless, unshielded, exposed, assailable, pregnable; unlocked, unsecured.
an insecure footbridge : UNSTABLE, rickety, rocky, wobbly, shaky, unsteady, precarious; weak, flimsy, unsound, unsafe; informal jerry-built; Brit. informal dicky, dodgy.
confident, stable.