S&P 500, e.g.

noun

1. A list of items (such as topics or names) treated in a printed work that gives for each item the page number where it may be found
2. A list of publicly traded companies and their stock prices
3. A bibliographical analysis of groups of publications that is usually published periodically
4. Thumb index
5. A number (such as a ratio) derived from a series of observations and used as an indicator or measure
6. The ratio of one dimension of a thing (such as an anatomical structure) to another dimension
7. A device (such as the pointer on a scale or the gnomon of a sundial) that serves to indicate a value or quantity
8. Something (such as a physical feature or a mode of expression) that leads one to a particular fact or conclusion indication
9. A number or symbol or expression (such as an exponent) associated with another to indicate a mathematical operation to be performed or to indicate use or position in an arrangement

   "3 is the index of the expression \sqrt[3] to indicate the cube root of 5"

10. A character ☞ used to direct attention to a note or paragraph
11. A list of restricted or prohibited material

verb

1. To provide with an index
2. To list in an index

   "all persons and places mentioned are carefully indexed"

3. To serve as an index of
4. To regulate (wages, prices, interest rates, etc.) by indexation
5. To index something

noun

1. The first documented case of an infectious disease or genetically transmitted condition or mutation in a population, region, or family

   "There were 54 cases of meningococcal disease in the 22 cluster schools, 30 of which occurred 1 or more days after the index case …"

2. An individual whose infectious disease or genetically transmitted condition or mutation is the first identified in a population, region, or family index patient

   "The index case was identified as a 20-year-old female student who had spent the winter break in a California county where there was a widespread community outbreak of measles. She returned to campus and became ill four weeks before the first case was reported."

3. the first documented case of an infectious disease or genetically transmitted condition or mutation in a population, region, or family
4. an individual whose infectious disease or genetically transmitted condition or mutation is the first identified in a population, region, or family : index patient

noun

1. The finger next to the thumb

noun

1. A fossil usually with a narrow time range and wide spatial distribution that is used in the identification of related geologic formations

noun

1. A number used to indicate change in magnitude (as of cost or price) as compared with the magnitude at some specified time usually taken as 100

noun phrase

1. Refractive index

noun

1. An individual affected with the first known case of an infectious disease or genetically transmitted condition or mutation in a population, region, or family index case

noun

1. A thin paper card used especially for creating an alphabetical index

   "kept recipes on index cards"