This article is from the alt.usage.english FAQ, by Mark Israel email@example.com with numerous contributions by others.
"Sirloin" comes from Old French "surlonge", from "sur" "above"
and "loigne" "loin". Its current spelling may have been influenced
by a story that a King of England (variously said to be Henry VIII,
James I, and Charles II) "knighted" this cut of beef because of
A "baron of beef" is a joint consisting of two sirloins left
uncut at the backbone. This "baron" may have originated as a joke
on "sirloin", or it may be an independent word.