Secret

1 Mystery
2 Enigma
3 Conceal
4 Veiled
5 Obscured
6 Hidden
7 Cloaked
8 Secret
9 Shadow
10 Covered
11 Camo
12 Masked
13 Eclipsed
14 Flagged
15 Clandestine
16 Unseen
17 Covert
18 Stealth
19 Incognito
20 Lurking