“En-” or “em-” as before a bilabial plosive like “broider” is all about placing things.  For example, one might place decorations – like braids or “browds” – on cloth with needlework.  Görlach notes that use of the prefix was pretty fluid in Early Middle English.  Tangent, the noun “embroider” can be the person who does the embroidery.

• 07.093 One bore a white cloth embroidered at the edges

“broider, v.” OED Online. Oxford University Press, June 2015. Web. 27 July 2015.

“† browd, v.” OED Online. Oxford University Press, June 2015. Web. 27 July 2015.

“embroider, v.” OED Online. Oxford University Press, June 2015. Web. 27 July 2015.

Görlach, Manfred. Introduction to Early Modern English. Cambridge: Cambridge University Press, 1991. Print.