资料来源 : pyDict

下面,下侧,底面

资料来源 : Webster's Revised Unabridged Dictionary (1913)

Underside \Un"der*side`\, n.
   The lower or lowest side of anything. --Paley.

资料来源 : WordNet®

underside
     n : the lower side of anything [syn: {bottom}, {undersurface}]