Quick definitions from WordNet (arch)

▸ noun:  (architecture) a masonry construction (usually curved) for spanning an opening and supporting the weight above it
▸ noun:  a passageway under an arch
▸ noun:  a curved bony structure supporting or enclosing organs (especially arches of the feet)
▸ noun:  a curved shape in the vertical plane that spans an opening
▸ verb:  form an arch or curve ("Her back arches")
▸ adjective:  (used of behavior or attitude) characteristic of those who treat others with condescension
▸ name:  A surname (very rare: popularity rank in the U.S.: #20407)

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▸ Also see arch