Lewis & Short

poppysma, ătis, n., and poppys-mus, i, m., = πόππυσμα and ποππυσμός, a smacking or clucking with the tongue, as a sign of approbation, Juv. 6, 584; on occasion of lightning, as a religious ceremony, Plin. 28, 2, 5, § 25; of a similar sound, Mart. 7, 18, 11.