Canto 1 - Boyhood
Bāla-kāṇḍa
Chapter 45: The Churning of the Milk Ocean
Text 1.45.33
अप्सु निर्मथनादेव रसस्तस्माद्वरस्त्रियः।
उत्पेतुर्मनुजश्रेष्ठ तस्मादप्सरसोऽभवन्॥
apsu nirmathanād eva rasas tasmād vara-striyaḥ
utpetur manuja-śreṣṭha tasmād apsaraso ’bhavan
apsu nirmathanāt eva = by churning the milk; rasaḥ = its essence appeared; tasmāt = from that essence; vara-striyaḥ = those excellent women; utpetuḥ = appeared; manuja-śreṣṭha = O best of men; tasmāt = therefore; apsarasaḥ = apsarās; abhavan = they were.
By churning the milk, its essence appeared. From that essence appeared those excellent women. O best of men, therefore, they were apsarās.
This explains the etymological derivation of the word apsarā. The extended meaning of ap (“water”) is its transformation in the form of milk. Its essence (rasa) was derived by churning the milk [in the milk ocean]. Because the apsarās appeared from that essence, they are called apsarās.