Something that is sphinxlike resembles a mythological creature which had a lion's body and a human head. A sphinxlike person is quiet, secretive, and mysterious.
The word sphinxlike is often used to describe people who are hard to figure out. What are they thinking as they sit in silence, looking at you with a calm expression that is hard to decipher? In a way, someone described as sphinxlike acts like a Sphinx, the clever, winged monster of Greek mythology who guarded the ancient city of Thebes by posing difficult riddles to those who wished to enter. A sphinxlike person is mysterious and, like a riddle, keeps everyone guessing.