1. (

• index ,
• index_number ,
• indicant ,
• indicator

) a number or ratio (a value on a scale of measurement) derived from a series of observed facts; can reveal relative changes as a function of time ;

2. (

• indicator ,

) a signal for attracting attention ;

3. (

• indicator

) a device for showing the operating condition of some system ;

4. (

• indicator

) (chemistry) a substance that changes color to indicate the presence of some ion or substance; can be used to indicate the completion of a chemical reaction or (in medicine) to test for a particular reaction ;