Besides the standard words such as dolphining, feeding, pacing, positioning and drafting, here are a few lesser known terms:
Alligator eyes: position of the head and eyes of an open water swimmer when he raises his head slightly over the surface of the water and looks forward in order to navigate.
Bioprene: hypodermis or subcutaneous tissue mainly used for fat storage and a natural means to help tolerate cold water (antonym: neoprene).
Beluga (slang): an athlete in the open water swimming community who weighs at least 200 pounds (analogous to a Clydesdale).
Channelversary: the annual recurrence of a date of one's channel swim.
Cap tan: the division on a swimmer's forehead between the skin of pronounced paleness relative to the rest of their face that has been suntanned by prolonged exposure to ultraviolet radiation in a pool, outdoors or in the open water.
Directional uncertainty: the lack of certainty about the optimal course or direction to take in an open water swim or triathlon swim leg. It's a state of having limited knowledge in a dynamic environment where it's difficult to know the optimal course.
Double capping: simultaneously wearing two swim caps in order to keep warmer in cold water.
Goggle tan: division on a swimmer's temple and around the eyes between skin of pronounced paleness relative to the rest of their face that has been suntanned by prolonged exposure to ultraviolet radiation in a pool, outdoors or in the open water.
Go to the gear: to grab one's hand paddles, pull buoys, snorkel, fins and/or kickboards after a hard main set in a pool workout or if the interval is too fast.
GWS drill: sprint and kick like a great white shark is in the water.
More: 2 Swim Sets for Speed
Hardening: the process of becoming acclimated to cold water.