The Collaborative International Dictionary of English v.0.48:

Size \Size\, v. t. [imp. & p. p. Sized; p. pr. & vb. n.
   Sizing.]
   To cover with size; to prepare with size.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sizing \Siz"ing\, n.
   1. Act of covering or treating with size.
      [1913 Webster]

   2. A weak glue used in various trades; size.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sizing \Siz"ing\, n.
   1. The act of sorting with respect to size.
      [1913 Webster]

   2. The act of bringing anything to a certain size.
      [1913 Webster]

   3. (Univ. of Cambridge, Eng.) Food and drink ordered from the
      buttery by a student.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sizing
    n 1: any glutinous material used to fill pores in surfaces or to
         stiffen fabrics; "size gives body to a fabric" [syn:
         size, sizing]