I'm doing a lot of defining these days, between widgetopia and a project I'm working. This defintion of "icon" is worth a honorable mention.

"Ultimately from Greek eikon (likeness, image, portrait), an icon (or ikon) is an image, a representation, a simile. Accordingly, 192 iconicity in a semiotic sense refers to signs where the motivation is due to some kind of physical resemblance or similarity between the signified and signifier (see section ); 193 a Christian icon is a picture of a sacred or sanctified personage, traditional to the Eastern Church, which can be seen as hand-made (painted) or non-manmade (archeiropoietos). 194 Semiotically incorrect, but nevertheless widely used, is the denomination of the symbols on the GUI desktop and in WWW documents as ''icons''. In this paper, I call the graphic representations of hyperlinks Graphical Link Markers (GLMs). "