What is yester?

Last semester, the previous semester of school

“I have to take psychology this semester”
“I took that yester semester and passed. It’s pretty easy.”

yester - meme gif

You promised me yester-last-year that you'd be be here within a year. It's too late now.

Being mired in thoughts and innovations of the past rather than forward-thinking.

I was so mired in yester-think that I didn't realize that technology was evolving all around me.

A term your English Teacher made up in order to describe the class you had yesterday.

"please refer to yester-lesson"

"Sir what are we doing today?"
"Continuing work from yester-lesson"

something that happend last night (instead of yesterday

you dog, yester-night i banged a girl

Nigel: I say, Basil, I had rather too much to drink yester-eve.
Basil: I suppose that would explain your vomiting this morn.

a slang term used in place of the word 'yesterday'

we had a little get together yesters.

"That chick that just yestered was hot!"
"Did you pass the yester test."