Dictionary.com
definitions

St. Andrew's cross

noun
  1. a cross composed of four diagonal arms of equal length; saltire.

Saint Andrew's Cross

noun
  1. an X-shaped cross.

St. Andrew's-cross

[an-drooz-kraws, -kros]
noun
  1. a low evergreen shrub, Ascyrum hypericoides, native to temperate and subtropical America, having flowers in clusters of three: often cultivated.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for st. andrew's cross

Saint Andrew's Cross

noun usually abbreviated to: St Andrew's Cross
  1. a diagonal cross with equal arms
  2. a white diagonal cross on a blue ground

Word Origin for Saint Andrew's Cross

C18: so called because Saint Andrew, one of the twelve apostles of Jesus, is reputed to have been crucified on a cross of this shape
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012