• ayādavīm — devoid of Yādavas
  Privative a- + yādavī. Jarāsandha's vow is the inversion of Kṛṣṇa's avatāra-prayojana: he wants a Yādava-less earth precisely while Kṛṣṇa is taking birth as a Yādava. The verse marks the head-on collision.
• śoka — sorrow
  Paired with amarṣa — grief seasoned with intolerant rage. Gauḍīya psychology: śoka without śaraṇāgati at Kṛṣṇa's feet metastasises into amarṣa, into war. The same śoka in Arjuna at Kurukṣetra becomes the doorway to Gītā only because he turns to Kṛṣṇa instead.
• udyamam — endeavor
  Paramam udyamam — the greatest possible endeavor. The demonic gather their armies in proportion to their hatred; the devotee gathers his sādhana in proportion to his love. Both are udyama; the difference is the object.

Like a man trying to empty the Yamunā with cupped hands, Jarāsandha vows to make the earth Yādava-less — yet every army he gathers is, unbeknownst to him, being assembled for Kṛṣṇa's harvest. The Lord uses His enemy's rage as a broom.