means A feeling of uncertainty, anxiety, or lack of confidence about oneself or one's circumstances; also, in a broader sense, the state of being unsafe or unprotected.

from Built from Latin securus — 'free from care,' itself a fusion of se- ('without') and cura ('care, worry'). Add the negating in- and you get the opposite: a mind that cannot stop caring, fretting, second-guessing. So 'insecurity' is, quite literally, a state of being un-free-from-worry. The word entered English by way of medieval Latin securitas, and where 'security' once meant carelessness in the sense of being untroubled, 'insecurity' kept the trouble and never let go.