The original word was Dhanush Koti (धनुष्कोटि)
कोटिः means the curved end of a bow
It is mentioned in Skanda Purana (स्कन्दपुराणम्) – Brahma Khanda, Setu- Khanda, chapter 30
सेतुनानेन ते राम राजानः सर्व एव हि ।।
बलोद्रिक्ताः समभ्येत्य पीडयेयुः पुरीं मम ।।
अतः सेतुमिमं भिंधि धनुष्कोट्या रघूद्वह ।।
इति संप्रार्थितस्तेन पौलस्त्येन स राघवः ।।
बिभेद धनुषः कोट्या स्वसेतुं रघुनं दनः ।।
अतो द्विजास्ततस्तीर्थं धनुष्कोटिरितिश्रुतम् ।।
When Rama had killed Ravana and made Vibhishana as new ruler of Lanka, than he along with Sita, Sugriva and Vibhishana went on to
Gandhamadana mountain. Vibhishana there requested Lord Rama that you please dismantle this bridge ( Ram – Setu ) using your sharp edge of your bow (धनुष्कोटि), otherwise various rulers will find easy to invade Lanka.
Since it was broken by Rama using sharp edge of his bow (धनुष्कोटि), therefore it is known as Dhanush Koti (धनुष्कोटि)
*****Dhanushkodi is an abandoned town at the south-eastern tip of Pamban Island of the state of Tamil Nadu in India.