Meaning of “assume” - Learner’s Dictionary

assume

verb [ T ] us uk /əˈsjuːm/
I assumed he was foreign.I assumed she meant later.You can't just assume that she understands.I assumed that you knew each other.He'd assumed we would be there.

B2 to think that something is likely to be true, although you have no proof:

[ + (that) ] Everything was quiet when I got home so I assumed that you had gone out.
assume control/power/responsibility, etc

to take a position of control/power/responsibility, etc:

He has assumed the role of spokesman for the group.
assume an air/expression, etc formal

to pretend to have a feeling that you do not have

assume a false identity/name, etc

to pretend to be someone else:

an assumed name

(Definition of “assume” from the Cambridge Learner’s Dictionary © Cambridge University Press)