What is the meaning of the word "shift"?

Definitions:

a crew of workers who work for a specific period of time noun
- No one wanted to be on the overnight shift, even though it paid better.
change gears verb
- You have to shift down when you go up a steep hill.
change in quality verb
- The speaker's tone shifted as the speech turned to more serious matters.
change phonetically as part of a systematic historical change verb
- Grimm showed how the consonants shifted
move and exchange for another verb
- shift the date for our class reunion
move from one setting or context to another verb
- shift the emphasis
move very slightly verb
- I shifted in my seat.
the act of changing one thing or position for another noun
- The shift from hunting and gathering to an agricultural based society was an important step on the road to modern organized production.
the act of moving from one place to another noun
- The student's constant shifts disrupted the class.
the key on the typewriter keyboard that shifts from lower-case letters to upper-case letters noun
- MY SHIFT BUTTON IS BROKEN AND NOW EVERYONE THINKS I AM YELLING AT THEM.
use a shift key on a keyboard verb
- i could not shift so all my letters are written in lower case.