adjective
lying behind what is manifest or avowed
an ulterior motive
Synonyms: buried, concealed, covert, guarded, hidden, obscured, privy, shrouded
Related Word: ambiguous, cryptic, dark, enigmatic, equivocal, obscure
Idioms: hidden under the rug, kept behind a screen, under cover, under wraps
Contrasted words: clear, open, overt, plain, straightforward; explicit, expressed