Many years ago when I was in grade school circa 1955, I became curious enough to look it up in Meriam- Webster. It defined Greensleeves as a grass stain that a male lover would get while propping himself on his elbows and fore arms. It also of course referred the reader to getting a green dress. If one assumes that this is metaphorical for someone who was sex smitten, then it adds some interesting interpretations to the lyrics. Interestingly when I went to look it up in later editions this meaning had vanished, but the term green dress lived on.