From Online Etymology Dictionary:
http://www.etymonline.com/index.php?term=solderSolder
c.1350, sawd, from O.Fr. soldure, from solder "to join with solder," from L.
solidare "to make solid," from solidus "solid" (see solid). Modern form is
from c.1420. The -l- is still pronounced in Great Britain. The noun is first
attested 1374.
Soder-on. :)
Ron Yost