**Stable**: Not subject to decline or reduction.

**Immutable**: Unchanging over time; unable to alter.

**Constant**: Remaining the same without variation.

**Enduring**: Lasting and persistent in existence or effect.

**Unyielding**: Firmly maintaining a level, unalterable by conditions.

**Permanent**: Lasting indefinitely without change or decrease.

**Resilient**: Able to withstand changes without diminishing quality.