aqua

1. Aqua (from ὠκεανός) denotes water materially as an element, in opp. to terra; unda (from νέδη, wet), as a flowing, continually moving element, in opp., as it were, to solum; lympha (λέμφος) is merely a poetical synonyme of aqua, with the accessory notion of clearness and brightness, to which the similar sound of the adjective limpidus, though not derived from it, gave occasion. 2. Unda stands in the middle, between aqua and fluctus, as aura does between aër and ventus. For unda denotes, like wave, that which apparently moves itself, whereas fluctus and fluenta, like billows, the water moved by something external, as storms and so forth; fluctus, the billows more in connection with the whole, the billowy sea, whereas fluentum denotes a single billow. It is only the stormy sea, the boisterous stream, that urges on its billows, but every piece of water, that is not entirely stagnant, has its waves. Hence there is a great distinction between these two images in Cicero, Mil. 2, 5. Tempestates et procellas in illis duntaxat fluctibus concionum semper putavi Miloni esse subeundas; that is, in the tumultuously agitated assemblies: and Planc. 6, 15. Si campus atque illæ undæ comitiorum, ut mare profundum et immensum, sic effervescunt quodam quasi æstu; that is, the lightly moving assemblies. Sen. N. Q. iii. 10. Quid si ullam undam superesse mireris, quæ superveniat tot fluctibus fractis. And iv. 2. Nec mergit cadens unda, sed planis aquis tradit. (ii. 10.)