The Collaborative International Dictionary of English v.0.48:

Solder \Sol"der\, n. [Formerly soder; F. soudure, OF. soudeure,
   fr. OF. & F. souder to solder, L. solidare to fasten, to make
   solid. See Solid, and cf. Sawder.]
   A metal or metallic alloy used when melted for uniting
   adjacent metallic edges or surfaces; a metallic cement.
   Hence, anything which unites or cements.
   [1913 Webster]

   Hard solder, a solder which fuses only at a red heat, as
      one composed of zinc and copper, or silver and copper,
      etc.

   Soft solder, a solder fusible at comparatively low
      temperatures; as, plumbers' solder, consisting of two
      parts lead and one part tin, is a soft solder.
      [1913 Webster]

WordNet (r) 3.0 (2006):

soft solder
    n 1: solder that melts at a relatively low temperature