not likely to fall or give way, as a structure, support, foundation, etc.; firm; steady.

able or likely to continue or last; firmly established; enduring or permanent

a stable government.

resistant to sudden change or deterioration

A stable economy is the aim of every government.

steadfast; not wavering or changeable, as in character or purpose; dependable.

not subject to emotional instability or illness; sane; mentally sound.

Physics . having the ability to react to a disturbing force by maintaining or reestablishing position, form, etc.

Chemistry . not readily decomposing, as a compound; resisting molecular or chemical change.

(of a patient's condition) exhibiting no significant change.

noun

fastness , firmness , hardness , security , soundness , steadiness , strength , sturdiness , sureness