1) Ageless 2) Ceaseless 3) Constant 4) Continual 5) Continued 6) Continuous 7) Endless 8) Enduring 9) Eternal 10) Everlasting 11) Immortal 12) Incessant 13) Lasting 14) Nonstop 15) Perennial 16) Permanent 17) Recurrent 18) Sustained 19) Timeless 20) Unceasing 21) Unending 22) Unremitting 1) Ageless 2) Eternal 3) Everlasting 4) French word used in English 5) Going on forever 6) Lasting 7) Permanent 8) Unceasing 9) Unending 
• (a.) Neverceasing; continuing forever or for an unlimited time; unfailing; everlasting; continuous.
An inventory accounting system updated for each addition to inventory and each issuance from inventory, so the records indicate the exact quantity on hand at any moment. The alternative is a periodic inventory system where actual inventory on hand is determined only once a year.
continual; never-ending
Per·pet'u·al adjective [ Middle English perpetuel , French perpétuel , from Latin perpetualis , from perpetuus continuing throughout, continuous, from perpes , -etis , lasting throughout.] Neverceasing; continuing forever or for an unlimited time; unfailing...
A security without a time limit for redemption. 
continuing forever or indefinitely continuing forever or indefinitely[PSAT glossary] continuing forever or indefinitely[Intelligent words] continuing forever or indefinitely[ACT vocabulary] continuing forever or indefinitely