双凸面 shuāng tū miàn

DEFINITIONS

  1. convex on both sides (of lens)
  2. biconvex

CHARACTERS

双 shuāng
HSK 3
set of two, pair, couple; both
凸 tū
HSK 6
protrude, bulge out, convex
面 miàn
HSK 1
face; surface; plane; side, dimension