Āpa & Āpo (nt.) [Vedic ap & āp, f. sg. apā, pl. āpaḥ, later Sk. also āpaḥ nt. -- Idg. *ap & *ab, primarily to Lith. ùpé water, Old Prussian ape river, Gr. *)lpi/a N. of the Peloponnesus; further (as *ab) to Lat. amnis river, Sk. abda cloud, & perhaps ambu water] water; philosophically t. t. for cohesion, representative of one of the 4 great elements (cp. mahābhūta), viz. paṭhavī, āpo, tejo, vāyo: see Cpd. 268 & Dhs trsl. 201, also below ˚dhātu. <-> D ii.259; M i.327; S ii.103; iii.54, 207; A iv.312, 375; Sn 307, 391 (˚ŋ), 392 (loc. āpe), 437 (id.); J iv.8 (paṭhavi -- āpa -- teja˚); Dhs 652; Miln 363 (gen. āpassa, with paṭhavī etc.); Sdhp 100.
   -- kasiṇa the water -- device, i. e. meditation by (the element of) water (cp. Mystic 75 n.) D iii.268; J i.313; Dhs 203; Vism 170; DhA i 312; iii.214. -- dhātu the fluid element, the essential element in water, i. e element of cohesion (see Cpd. 155 n. 2; Mystic 9 n. 2; Dhs trsl. 201, 242) D iii.228, 247; M i.187, 422: Dhs 652; Nett 74. See also dhātu. -- rasa the taste of water A i.32; SnA 6. -- sama resembling water M i.423.

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