stackronym

A stackronym is an acronym built using other acronyms.

A stackronym is not the same as a recursive acronym, which is an acronym built with itself as part of the acronym.

AIM - AOL Instant Messenger
AOL - America Onine
AIM = America Online Instant Messenger

GTK+ - GIMP Toolkit
GIMP - GNU Image Manipulation Program
GNU - GNU's Not Unix
GTK+ = GNU's Not Unix Image Manipulation Program Toolkit