opāna : [nt.] a well; place where water is supplied free.

A.P. Buddhadatta Mahathera, Concise Pali-English and English-Pali Dictionary [available as digital version from Metta Net, Sri Lanka]

Opāna (nt.) [o + pāna fr. pivati. Vedic avapāna. The P. Commentators however take o as a contracted form of udaka, e. g. Bdhgh. at DA i.298 = udapāna]. Only in phrase opāna -- bhūta (adj.) a man who has become a welling spring as it were, for the satisfaction of all men's wants; expld. as "khata -- pokkharaṇī viya hutvā" DA i. 298 = J v.174. -- Vin i.236; D i.137; M i.379; A iv. 185; Vv 654; Pv iv.160; J iii.142; iv.34; v.172; Vbh 247; Miln 411; Vism 18; VvA 286; DA 1177, 298.

Pali-English Dictionary, TW Rhys Davids, William Stede,