Open English Wordnet
Verbs
Adjectives
(a)secure, unafraid, untroubledfree from fear or doubt; easy in mind“he was secure that nothing will be held against him”
(s)impregnable, inviolable, secure, strong, unassailable, unattackableimmune to attack; incapable of being tampered with“an impregnable fortress”, “fortifications that made the frontier inviolable”, “a secure telephone connection”