Invariable (adjective)

Not liable to change or variation; constant.

Origin:

Late latin invarīabilis, from latin in- + varīabilis variable.

Examples:

1. The speed of light is an invariable constant.
2. The sales process has become an invariable routine for the sales team.
3. Her mood was invariable and always positive.
4. Despite its popularity, the recipe for the dish remains invariable.
5. The company's policy on dress code is invariable and strictly enforced.