ताभ्याम् both of them, उभाभ्याम् one over the other, तरसा swiftly, प्रसृष्टैः extended, शितैः whetted, विशिखैः arrows, निरन्तरमिव continuously, आकाशम् the sky, तमसा dark, वृम् shrouded, बभूव became

while both of them one over the other swiftly extended and loosened the whetted arrows continuously, the sky, shrouded with arrows, became dark.