hermetic (adj.)
- abstruse
- airtight
- arcane
- bombproof
- bulletproof
- burglarproof
- cabalistic
- censored
- classified
- cloistered
- close
- closed
- compact
- concealed
- cryptic
- dark
- deep
- enigmatic
- esoteric
- fast
- fire-resisting
- fireproof
- firm
- flameproof
- foolproof
- heavy
- hidden
- hush-hush
- impervious
- latent
- leakproof
- lightproof
- mysterious
- occult
- profound
- proof
- rainproof
- recluse
- resistant
- restricted
- rustproof
- sealed
- secret
- sequestered
- shatterproof
- shellproof
- smothered
- snug
- soundproof
- staunch
- stifled
- stormproof
- suppressed
- tight
- ulterior
- undisclosed
- unrevealed
- unspoken
- untellable
- untold
- unutterable
- unuttered
- waterproof
- watertight
- weatherproof
