Invariable

In*va"ri*a*ble (?), n. (Math.) An invariable quantity; a constant.

In*va"ri*a*ble (?), a. [Pref. in- not + variable: cf. F. invariable.] Not given to variation or change; unalterable; unchangeable; always uniform.

Physical laws which are invariable.
I. Taylor.

-- In*va"ri*a*ble*ness, n. -- In*va"ri*a*bly, adv.