# residue

Pronunciation: US say "REZ-i-doo" /ˈɹɛzɪduː/; UK say "REZ-i-dyoo" /ˈɹɛzɪdjuː/

## Noun

1. The part that is left behind once something else has been taken away or used up.
   - Simple: The part that is left when everything else has been taken away.
   - _A sticky residue coated the jar long after the honey was gone._
   - _Cleaning sprays often leave a faint residue on glass surfaces._
2. Material left behind when a liquid is removed or a mixture is separated, for example by filtration, evaporation, or distillation.
   - Simple: The stuff left behind after a liquid dries up, boils away, or is filtered out.
   - _After distillation, the chemist weighed the residue at the bottom of the flask._
   - _Evaporating the seawater leaves a salty residue rich in minerals._
3. The property and effects left in an estate after all debts and charges are paid and specific bequests are deducted.
   - Simple: What is left of a dead person's money and property after all debts and gifts are paid.
   - _Under the will, the residue passes to the testator's surviving children._
   - _The executor distributed the residue once every creditor had been settled._
4. A molecule, such as an amino acid in a polypeptide chain, released from a polymer when the bonds between neighboring monomers are broken.
   - Simple: A single building-block molecule, such as an amino acid, left when a long chain is broken apart.
   - _The enzyme cleaves the polypeptide, freeing one amino acid residue at a time._
   - _Each residue in the chain contributes to the protein's final folded shape._
5. The nonnegative remainder left after dividing a number by a base; a representative of an equivalence class modulo that base, usually taken between zero and the base.
   - Simple: The whole number left over after you divide one number by another.
   - _Working modulo 7, the number 23 has a residue of 2._
   - _Each integer reduces to a unique residue in the range zero to four when working modulo five._
6. A complex number associated with a singularity of a meromorphic function, proportional to the contour integral of the function along a path enclosing that point.
   - Simple: A special number tied to a point where a function breaks down, worked out by looping around that point.
   - _She computed the residue of the function at its simple pole._
   - _Summing each residue inside the loop gives the value of the contour integral._

## Origin

This word came through Middle English and Old French residu from Latin residuum, the neuter of residuus ("remaining"), which derives from resideō ("I remain behind"). It is a doublet of residuum.

Source: DictionaryAI, https://dictionaryai.com/define/residue (written from Wiktionary data, CC BY-SA 4.0: https://creativecommons.org/licenses/by-sa/4.0/).