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1.
Derived from the freshwater fish that feeds on scraps in the murky depths of gravel pits/ponds accross europe, a Tench is a selfish bloke who knowingly and unwitingly goes out of his way to feed off the bottom and steal his friends birds/shags. AKA bottom feeder.
My mate saw you last nite Johnny, steaming in to my ex bird you fuckin Tench
by moogfish June 01, 2006
 
2.
1.) A brown, lake-bottom loving freshwater fish.
2.) A heavy and persistent turd which hugs the bottom of the bowl before finally being sent on its way after the tenth flush.
'Right, who left that tench in the bog?'
by Steve September 23, 2003
 
3.
A person who has the potential to be one's future girl/boyfriend. Often identified by obvious flirting.

Tenchtench: someone's potential to become tench. It is less so than tench.
She is major tench
by grimer13 July 13, 2011
 
4.
Maybe
"Do you wanna go to the mall tomorrow?"
"Tench."
by lululululululululululululululu February 21, 2012
 
5.
Adjective used to denote something as being good to the max. In the same form as tasty and tight.
After the scoring of a particularly excellent goal it is common to say "That goal was proper tench man!" to golden balls.
by RobinAldworth March 15, 2007