John Wilkins has pointed me to a couple of good articles2 on the proper use of the word "homology': Distant homology and being a little pregnant and 2010 Homology High-Low Count.
The first article explains why the term "structural homology" should be banned from the scientific literature. The correct term is "structural similarity."
The meaning of homology is on my mind lately because I'm grading essays that critique Jonathan Wells' book Icons of Evolution. Student have to pick one of the chapters and analyze the arguments used by Wells to attack evolution. One of the chapters is "Homology in Vertebrate Limbs" and it's one of the most difficult chapters because Wells highlights the frequent misuse of "homology" in the scientific literature.
1. I have many. It's what happens when you get old.
2. I wonder if he's doing this on purpose—posting a list of provocative articles in the hopes that someone else will do all the work?