The Collaborative International Dictionary of English v.0.48:

Form \Form\, v. i.
   1. To take a form, definite shape, or arrangement; as, the
      infantry should form in column.
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   2. To run to a form, as a hare. --B. Jonson.
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   To form on (Mil.), to form a lengthened line with reference
      to (any given object) as a basis.
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