reflux

noun

1. (countable, uncountable)The backwards flow of any fluid.

   “[…] after a little way out to sea, there was a current and wind, always one way in the morning, the other in the afternoon. This I understood to be no more than the sets of the tide, as going out or coming in; but I afterwards understood it was occasioned by the great draft and reflux of the mighty river Orinoco […]”

2. (countable, uncountable)A technique, using a reflux condenser, allowing one to boil the contents of a vessel over an extended period.
3. (countable, uncountable)The leaking of stomach acid up into the oesophagus.

verb

1. To flow back or return.

   “the refluxing tide”

2. To boil a liquid in a vessel having a reflux condenser.