Ah, what a delightful question! The word you're looking for is "safe." A safe is a special box designed to protect and secure your money and other valuable treasures. Keep on creating, my friend!
Cash
Safe.
cash
cash
Hide.
sell
kale, keep, kite, kiss
Keep and kelp are four letter words starting with K and ending with P.
Kind, kill, keep, kink, kook
A four letter word starting with the letter a is able.
A four letter word for 'in addition to' is also.
Lard is a four letter word for grease.