Synonyms of the word 
LOCKBOX → SAFE-DEPOSIT - STRONGBOX
lockbox
- n. A box with a built-in lock; a safe.
safe-deposit
- adj. Safe enough to store valuables securely.
- n. A safe-deposit box.
strongbox
- n. A sturdy box with a lock for keeping valuables in.
If you are interested in words, visit the following sites :
- wiktionary.org/lockbox For complete definition of a word
- 1word.ws/lockbox to play with words, suffixs, prefixs, etc.