In a manner relating to or characteristic of burglary; illegally entering and stealing.
From burglarious + -ly (adverb suffix). Follows standard English adverbial formation from adjectives.
This adverb is so rare that you'll almost never see it in real English—it's the kind of word that exists in dictionaries but judges probably wouldn't use even in formal court documents.
Complete word intelligence in one call. Free tier — 50 lookups/day.