If you're looking for cases or statutes that define a term, rather than all cases that mention the term in any context, search for WP(term), e.g.,

WP("DANGEROUS WEAPON")

This only works for those terms that West includes in its "Words and Phrases" books; but that's a pretty large set of terms.

Naturally, searching for all references to the term, rather than just for the WP() references, will give you a more complete list. But it may be far too complete, giving you thousands of cases. WP() searching will knock out many of the false positives, though at the risk of omitting some of the true positives.

Maybe most of you know about this feature or already, but some experienced lawyer and law professor friends I asked hadn't, so I thought I'd pass it along in case many people are unfamiliar with it. For similar tips about ATLEAST, NOT W/, and SY,DI(), see here.