1 countable something that you think is true although you have no definite proof
A. assumption that
B. assumption about

2 uncountable formal when someone starts to have control or power
A. assumption of
1. A lot of people make the assumption that poverty only exists in the Third World.
My calculations were based on the assumption that house prices would remain steady.
We are working on the assumption that the conference will take place as planned.
B. People make a lot of assumptions about me.
underlying assumption (=a belief that is used as the basis for an idea, but which may not be correct)

2. the assumption of responsibility
by ELLIOT TINTAS November 24, 2011
The Brother of all fuck-ups.
Soap: Oh you assume do ya? And what do they say about assumption being the
brother of all fuck-ups?
Tom: It's the mother of all fuck-ups, stupid...
by dip June 29, 2004
assuming two people like each other based on their flirtatious encounters.
omg yeahh! ASSUMPTIONSS!
To assume or make a guess either false or true
assumption is a word created by ants
by Antzzzzz September 25, 2005
to make an assumption is to make an ass of u and mption
u: i made an assumption
mption: rly bruh
by LudwigVonPhoenix October 25, 2019
You don't want to make an assumption because you will be and ASS-and your-UMP- will-TION- you
You will think a little harder before you make another assumption.
by Chris h to hissy h June 21, 2005