CC Ādi 4.87
ataeva ‘rādhikā’ nāma purāṇe vākhāne
Her worship [ārādhana] consists of fulfilling the desires of Lord Kṛṣṇa. Therefore the Purāṇas call Her Rādhikā.
The name “Rādhā” is derived from the root word ārādhana, which means “worship.” The personality who excels all in worshiping Kṛṣṇa may therefore be called Rādhikā, the greatest servitor.