त्वाम् you, अभिनिघ्नता by killing you, रामेण by Rama, महत् great, कर्म deed, कृतं हि accomplished, सुग्रीवस्य for Sugriva, प्रतिश्रवे in fulfilling promise, तस्य his, आनृण्यम् debt, गतं तु is acquitted.

'Indeed, Rama has achieved a great feat in fulfilling his promise to Sugriva. He is acquitted of the debt by killing you.