In the excerpt from the speech about which I wrote here, Thomas Fingar describes how the IC defined a nuclear explosive device:

DR. FINGAR: The judgment in the estimate – and I’m not going beyond what’s sort of in the unclassified, if you actually read it and understand what you’re reading here – we didn’t change the timeline on how long they would have fissile material. We didn’t change our timeline on how long it would take them to have a device – a device is something like the North Koreans have; it will go bang underground; it will go bang someplace; harder to make it deliverable and to get it small. But though there is a lot that we do not know about how far along they were in this process

Yes, I know he didn’t use that exact phrase, but I think mine is a reasonable interpretation.