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1.
To get (very) drunk

Also 'to go on the lash'.

Synonymous with:
Get pissed, get wasted, get hammered, get rat-arsed, get sloshed, get trolleyed etc

The word 'lash' orinally means to strike with a whip, and so has this extended meaning (ie. drinking makes you feel like you've been flogged).
NB. Usually used in a positive sense.
1. "Hey John, what are you up to tonight? The boys are all going out and getting lashed"

2. "The boys are all going out on the lash tonight."
by zimman August 02, 2005