Valmiki Ramayana Sundara Kanda Sarga 1 Shloka 10
Original Shlokaप्लवङ्गप्रवरैर्दृष्टः प्लवने कृतनिश्चयः। ववृधे रामवृद्ध्यर्थं समुद्र इव पर्वसु।।5.1.10।।
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प्लवङ्गप्रवरैः the monkey troops, दृष्टः were gazing, प्लवने taking leap, कृतनिश्चयः resolved, पर्वसु during the fullmoon days, समुद्रः इव like the sea, रामवृद्ध्यर्थम् for the welfare of Rama, ववृधे began to grow in size.
Having made up his mind to leap for the cause of Rama, Hanuman began to grow in size just as the sea grows during the fullmoon and newmoon days, while the monkey troops were watching.