There actually isn't a Sindarin word for flood. The Sindarin name for the river Greyflood is Gwathló which directly translates as Pool of Shadow. The river that feeds into it is Mitheithel which means Grey Well.
You could of course use any word for pool, river, or other body of water to denote Greyflood.
Grey: mithren, thind
Pale grey: mith
river: celon, sîr
great river: sirion
large river: duin
pool: ael, lîn, loeg, nên
cold pool: rim
small pool: bôth
Mithgelon, Mithír, Mithirion, Mithduin, Mithael, Mithlín, Mithloeg, Mithnen, Mithrim, Mithboth, Thingelon, Thinhír, Thinduin, Thindael, Thinglín, Thingloeg, Thinnen, Thidhrim, Thimboth, Mithrengelon, Mithrenhír, Mithrenhirion, Mithrenduin, Mithrenael, Mithrenglín, Mithrengloeg, Mithrennen, Mithredhrim, Mithremboth.
Obviously a lot of those are a mouthful. Now the Hast that you added actually means axe-stroke. If you were looking for axe that is Hathol, which makes it even more of a mouthful.
(Note: following an -r or vowel, h- becomes ch-)
Aer Baul (or Aerbol) would actually be Torment of the Sea; however, that still fits your name. (And you shouldn't "breeze" an Orc . . . it could be dangerous.

) The word you are looking for is Gaer (dreadful, awful, holy) . . . following the imperative verb No (be), it lenits to Aer. In this case, it would be Gaerbol.