
• (n.) A long piece of timber, forming a margin or edge of any piece of construction; esp.: • (n.) One of the longitudinal pieces, supporting the treads and rises of a flight or run of stairs.
Found on
http://thinkexist.com/dictionary/meaning/stringpiece/
String'piece` noun (Architecture) (a) A long piece of timber, forming a margin or edge of any piece of construction; esp.:
(b) One of the longitudinal pieces, supporting the treads and rises of a flight or run of stairs.
Found on
http://www.encyclo.co.uk/webster/S/211

In architecture a stringpiece is a long piece of timber, forming a margin or edge of any piece of construction but especially applied to one of the longitudinal pieces, supporting the treads and rises of a flight or run of stairs.
Found on
http://www.probertencyclopaedia.com/browse/TS.HTM

a long, usually horizontal piece of timber, beam, etc., for strengthening, connecting, or supporting a framework.
Found on
https://www.infoplease.com/dictionary/stringpiece
No exact match found.