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.
Synonyms for the verb/adjective 'concealed' are:coveredhiddenmaskedobscuredsecreted
Another word would be drenched, coated or smothered.
help sir
hidden, invisible, unseen