Surfaces antonyms

What is the opposite word for Surfaces?

• personality

  external part of something
• core

  external part of something
• interior

  external part of something
• middle

  external part of something
• character

  external part of something
• disappear

  come to the top of
• dive

  come to the top of
• inside
• center
• submerge

  come to the top of
• 

  drop

  come to the top of
• fall

  come to the top of
• sink
• insides
• characters
• cores
• interiors
• middles
• personalities
• centers
• centres
• sinks
• drops
• falls