Dictionary.com
definitions

piss

[pis]Vulgar.
noun
  1. urine.
verb (used without object), pissed, piss·ing.
  1. to urinate.
Idioms
  1. piss away, Slang. to squander; fritter away:
  2. piss off, Slang.
    1. to anger.
    2. to go away; leave (often used imperatively).
  3. take a piss, to urinate.

Origin of piss

1250–1300; Middle English pissen < Old French pissier < Vulgar Latin *pisiāre (imitative)
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for piss away

piss

verb
  1. (intr) to urinate
  2. (tr) to discharge as or in one's urineto piss blood
noun
  1. an act of urinating
  2. urine
  3. Australian beer
  4. on the piss drinking alcohol, esp in large quantities
  5. piece of piss something easily obtained of achieved
  6. take the piss to tease or make fun of someone or something
  7. piss all over to be far superior toa version that pisses all over the original

Word Origin for piss

C13: from Old French pisser, probably of imitative origin
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Word Origin and History for piss away

piss

v.

late 13c., from Old French pissier "urinate" (12c.), from Vulgar Latin *pissiare, of imitative origin. To piss away (money, etc.) is from 1948. Related: Pissed; pissing. Pissing while (1550s) once meant "a short time."

He shall not piss my money against the wall; he shall not have my money to spend in liquor. ["Dictionary of Buckish Slang, University Wit and Pickpocket Eloquence," London, 1811]

piss

n.

late 14c., from piss (v.). As a pure intensifier (piss-poor, piss-ugly, etc.) it dates from World War II. Piss and vinegar first attested 1942. Piss-prophet "one who diagnosed diseases by inspection of urine" is attested from 1620s. Piss proud "erect upon awakening" is attested from 1796.

Online Etymology Dictionary, © 2010 Douglas Harper
Idioms and Phrases with piss away

piss away

Squander, waste, as in They've pissed away a fortune on those horses. This term uses piss in the sense of “discharge something as though it were urine.” [Vulgar slang; first half of 1900s]

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.