How word Rishikesh (ऋषिकेश) was formed ?
This word “ऋषिकेश” was formed due to wrong pronunciation of original word “हृषिकेश”
हृषिकेश (Hrishikesh) means the Lord of senses, Vishnu
हृषीकाणाम् (इन्द्रियाणाम्) ईश: हृषीकेशः ( षष्ठी तत्पुरुष समास )
हृषीक + ईश: = हृषीकेशः (गुण सन्धि )
Example of गुडाकेशः
Similarly there is another word called गुडाकेशः – meaning the one who has conquered sleep, Shiva , Arjun
गुडाकायाः निद्रायाः ईशः ( षष्ठी तत्पुरुष समास )
गुडाका means Sleep
गुडाका + ईशः = गुडाकेशः (गुण सन्धि )
Reference in Bhagavata Gita:
These both words are mentioned in Bhagavata Gita 2.9
एवमुक्त्वा हृषीकेशं गुडाकेशः परन्तप।
न योत्स्य इति गोविन्दमुक्त्वा तूष्णीं बभूव ह ।
“Sanjaya said: Having spoken thus, Arjuna, chastiser of enemies, told Krishna, “Govinda, I shall not fight,” and fell silent.”