a device for showing the operating condition of some system
a signal for attracting attention
(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
engaged in as a pastime; "an amateur painter"; "gained valuable experience in amateur theatricals"; "recreational golfers"; "reading matter that is both recreational and mentally stimulating"; "unpaid extras in the documentary"