We made small talk, the cops and I, about the July Fourth fireworks and the weather, while my hands were tested for gunshot residue
and the slick inside of my cheek was cotton-tipped.
Gillian Flynn -- Gone Girl
what remains after the main part is gone
Specialized senses of residue
- chemistry: remaining substance after evaporation, distillation, filtration or any similar process
- law: residue, residual estate, residuary estate, or residuum reference that part of a dead person’s money and property that is left after all debts, and specific bequests have been fulfilled.
See Wikipedia - Residue (other)
to link to a discussion of these and other specialized senses.