The Collaborative International Dictionary of English v.0.48:

Arch \Arch\, v. t. [imp. & p. p. Arched ([aum]rcht); p. pr. &
   vb. n. Arching.]
   1. To cover with an arch or arches.
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   2. To form or bend into the shape of an arch.
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            The horse arched his neck.            --Charlesworth.
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The Collaborative International Dictionary of English v.0.48:

Arching \Arch"ing\, n.
   1. The arched part of a structure.
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   2. (Naut.) Hogging; -- opposed to sagging.
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WordNet (r) 3.0 (2006):

arching
    adj 1: forming or resembling an arch; "an arched ceiling" [syn:
           arced, arched, arching, arciform, arcuate,
           bowed]