1.
If you ~ something such as an engine or an electrical item, you turn it off to stop it working.
They pulled over and ~ the engine...
Will somebody for God’s sake shut that alarm off.
= switch off
PHRASAL VERB: V P n (not pron), V n P
2.
If you shut yourself off, you avoid seeing other people, usually because you are feeling depressed.
Billy tends to keep things to himself more and shut himself off...
PHRASAL VERB: V pron-refl P
3.
If an official organization shuts off the supply of something, they no longer send it to the people they supplied in the past.
The State Water Project has ~ all supplies to farmers.
PHRASAL VERB: V P n (not pron), also V n P