Hidden, covered, censored, blocked
Hidden
hidden
hide
covert unseen hidden masked disguised
covert, hidden, unseen
gunman, assassin, sniper,
sheltered, private, concealed, hidden, unfrequented, sequestered
If you mean letters, it's hidden.
Another word for conceal is to hide, disguise and hold back.
Another word would be drenched, coated or smothered.
help sir
hidden, invisible, unseen