Synonyms for Hidden (same or very similar meaning)
WordNet sense 1 (not accessible to view):
out of sight
WordNet sense 2 (impossible or nearly impossible to see; imperceptible by the eye):
invisible, unseeable
WordNet sense 3 (designed to elude detection):
secret
WordNet sense 4 (difficult to find):
obscure
WordNet sense 5 (hidden on any grounds for any motive):
concealed
From the ODE community, based on WordNet
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