If you are staunchly loyal, you are true blue. Why?
In medieval times when cloth was made by hand, its fibers were dyed with various blossoms, berries, and bark. The dyes often faded after many washings, however. Blue was the most difficult color to hang on to.
But not so for the blue dye used in Coventry, England. Here, artisans had found the formula for a long-lasting blue - called Coventry blue - that remained bright. For years, this permanent, or "true blue" remained the best on the market and "as true as Coventry blue" came to mean faithful and constant. A color you could depend on!
In the 10th century, the Anglo-Saxon stedefoest (fixed in position) referred to soldiers, whose duty it was to guard a town.
"Stead" comes from the Anglo-Saxon stede (place) and the German stadt (town). "Fast" derives from the German fest (firm) and the verb fastu (to keep or guard).
Nowadays, steadfast is more commonly used to mean "loyal and unwavering."
SOURCES: 'Why You Say It,' by Webb Garrison; 'A Dictionary of Contemporary American Usage,' by B. and C. Evans; 'The Barnhart Dictionary of Etymology,' by Robert K. Barnhart; 'Brewer's Dictionary of Prose and Fable,' revised by Ivor H. Evans; 'Horsefeathers,' by Charles E. Funk.