Amoghārtha is one of the Aṣtottara Sahasranāma(Ashtottara Sahasranama; Thousand and Eight Names) of Śiva-Mahādeva (Siva-Mahadeva). Amogha means something that is absolute, and never goes in vain. And Artha means ‘to pray, to want, to desire’.
Bevolent to his devotees, Śiva keeps no desire of them unfulfilled. All the desires of his devotees get fulfilled by His grace, so He is called Amoghārtha —
artho’rthanaṃ yācñā amogho’rtho .