1
concluir;conjeturar;presumir;regañar
1
to fix upon (one-sidedly);to (ignore someone's position and) arbitrarily decide something is the case
そういうの、先入観っていうんだよっ！体験したこと無いのに、決め付けるのはよくないっ！
That's what they call 'prejudice'! It's wrong to make your mind up on something you've never experienced!
2
to scold;to take (a person) to task
上司は僕の仕事振りがいい加減だと決め付けた。
My boss took me to task for the poor quality of my work.
Other forms
決めつける 【きめつける】