The feature key is the Mac's equivalent of a control key (and so labelled on some Mac II keyboards). The proliferation of terms for this creature may illustrate one subtle peril of iconic interfaces. Macs also have an "Option" modifier key, equivalent to Alt.
The cloverleaf-like symbol's oldest name is "cross of St. Hannes", but it occurs in pre-Christian Viking art as a decorative motif. In Scandinavia it marks sites of historical interest. An early Macintosh developer who happened to be Swedish introduced it to Apple. Apple documentation gives the translation "interesting feature".
The Swedish name of this symbol stands for the word "sev"ardhet" (interesting feature), many of which are old churches. Some Swedes report as an idiom for it the word "kyrka", cognate to English "church" and Scots-dialect "kirk" but pronounced /shir'k*/ in modern Swedish. Others say this is nonsense.