Charybdis
Maelstrom
back stream
backwash
backwater
countercurrent
counterflow
counterflux
eddy
gulf
gurge
maelstrom
refluence
reflux
regurgitation
swirl
twirl
vortex
whirl
whirlpool
flow
flowing
back pressure
closed-center
composted
defrost
derichment
feculent
gastroesophageal
nonbattle
pharmacologic
semilunar
sliding-spool
solenoid-operated
tainting
tricuspid
ultra-precision