invariable

Not variable; unalterable; uniform; always having the same value.not-comparable

• Physical laws which are invariable.
• “A tight little craft,” was Austin’s invariable comment on the matron; and she looked it, always trim and trig and smooth of surface like a converted yacht cleared for action.

Constant.not-comparable

That cannot undergo inflection, conjugation or declension.broadlynot-comparable

• The French adjective marron ‘brown’ is invariable: it does not take the usual s in the plural.

Something that does not vary; a constant.