अन्वयः

पर्वणि on the day of the full Moon and new Moon, समुद्र इव like sea, वीर्येण with energy, विवर्धमान: growing, ऋषिसत्तमम् foremost of ascetics, वसिष्ठम् Vasishta, तदा then, हतमेव slain only, मेने thought over.

M N Dutt

Surcharged with energy, like to the sea during the equinox, he considered, O Rāma, as if that foremost of saints, Vasistha, was already slain.

Summary

Like the sea during the full moon, with his increased power (blessed with the invincible strength of the weapons) Viswamitra thought the foremost of ascetics Vasishta was (already) slain. (It shows the height of the king's ignorance and arrogance).

पदच्छेदः

विवर्धमानो	विवर्धमान (√वि-वृध् + शानच्, १.१)
वीर्येण	वीर्य (३.१)
समुद्र	समुद्र (१.१)
इव	इव (अव्ययः)
पर्वणि	पर्वन् (७.१)
हतम्	हत (√हन् + क्त, २.१)
एव	एव (अव्ययः)
तदा	तदा (अव्ययः)
मेने	मेने (√मन् लिट् प्र.पु. एक.)
वसिष्ठम्	वसिष्ठ (२.१)
ऋषिसत्तमम्	ऋषि–सत्तम (२.१)

छन्दः

अनुष्टुप् [८]

छन्दोविश्लेषणम्

१	२	३	४	५	६	७	८
वि	व	र्ध	मा	नो	वी	र्ये	ण
स	मु	द्र	इ	व	प	र्व	णि
ह	त	मे	व	त	दा	मे	ने
व	सि	ष्ठ	मृ	षि	स	त्त	मम्