lock up

In printing, to combine all the letterpress printing elements, including type and plates, in a single unit, called a form, and then to position the form in a rectangular metal frame, called a chase, so that the entire unit is ready for printing.

1.  Close a house or place of work, fastening all the doors and windows, as in The attendant locks up at eleven o'clock every night, or Did you remind Abby to lock up? [Late 1500s]
2.  Invest in something not easily converted into cash, as in Most of their assets were locked up in real estate. [Late 1600s]
3.  lock someone up. Confine or imprison someone, as in The princes were locked up in the Tower of London. [c. 1300]

The verb has 2 meanings:

Meaning #1: secure by locking

Meaning #2: place in a place where something cannot be removed or someone cannot escape
  Synonyms: lock in, lock away, lock, put away, shut up, shut away