inelastic (adj.)

• adamant
• adamantine
• cast-iron
• dour
• firm
• flinty
• grim
• hard
• hard-core
• immovable
• immutable
• implacable
• inexorable
• inextensible
• inflexible
• intractable
• intransigent
• iron
• irreconcilable
• relentless
• rigid
• rigorous
• rock-ribbed
• steely
• stern
• stiff
• stubborn
• unaffected
• unalterable
• unbending
• unchangeable
• uncompromising
• unmalleable
• unmoved
• unrelenting
• unyielding