flatten
     v 1: make flat or flatter; "flatten a road"; "flatten your
          stomach with these exercises"
     2: become flat or flatter; "The landscape flattened" [syn: {flatten
        out}]
     3: lower the pitch of (musical notes) [syn: {drop}] [ant: {sharpen}]
Source: WordNet® 2.0

flatten vt. [common] To remove structural information, esp. to filter
   something with an implicit tree structure into a simple sequence of
   leaves; also tends to imply mapping to {flat-ASCII}. "This code flattens
   an expression with parentheses into an equivalent {canonical} form."


Source: The Jargon File