1A thing that indicates the state or level of something.

1. 1.1 An animal or plant species that can be used to infer conditions in a particular habitat.
   the raccoon is a poor choice as an indicator of riparian habitat

   Example sentencesExamples

   • ‘They are important indicator species,’ he says.
   • The minnow is an indicator species that suggests the overall health, or sickness, of the entire river ecosystem.
   • Marine predators are in general decline worldwide and this is what makes seals such a key indicator species.
   • The plant associates are common widespread wetland species in the southeastern United States, and none were determined to be indicator species.
   • Now it and various other indicator species are probably doomed.
   • Research indicated the owl is an indicator species whose decline indicates the imperilment of the old-growth forest ecosystem.
   • We suggest that this tree species should be considered an indicator species with unexplored economic potential.
   • For this reason, Black-legged Kittiwakes have been proposed as a good indicator species of marine health.
   • This also involved the villagers taking on the responsibility of monitoring the key indicator species to understand how the regeneration process was taking place.
   • The calanoid copepod Lucicutia grandis is an indicator species for this habitat.
   • Decline of river fish is yet another indicator that natural habitats such as wetlands and rivers and the life they sustain are under intense pressure.
   • They're what botanists would call an indicator species.
   • ‘The pygmy hog is an important indicator species, and we need to know why it is disappearing faster than other less sensitive species,’ he said.
   • The indicator species can either be observed directly on the ground by exploration geochemists or detected indirectly in aerial photographs or satellite images.
   • We also look at them as indicator species more and more.
   • Are they an indicator species, a harbinger of global environmental crashes ahead?
   • Repeat the watering when the indicator plants again wilt.
   • Relatively high levels of pesticides have been found in some western populations, and Tree Swallows are often used as indicator species for pollutants.
   • It's a so-called indicator species that lives in the river.
   • So they are terribly important as kind of indicator species of our environment.

2usually with modifier A gauge or meter of a specified kind.

1. 2.1British A flashing light or (formerly) other device on a vehicle to show that it is about to change lanes or turn.
   as modifier an indicator light

   North American term turn signal

   Example sentencesExamples

   • This cluster would also feature normal orange indicators and white reversing lights but which cannot be seen within the red tail light cluster when not in operation.
   • And, as with some Asian cars, the indicator and windscreen wipers are reversed, which can cause no end of confusion at first,
   • In the end, the driver crawled along until he could get into a lay-by using only his indicator light for illumination, and used his own mobile to call the police.
   • Conventional car lighting has a number of elements - headlamps, indicators, brake lights - in set positions.
   • The bike had no horn, indicators, no lights, no rear brakes, and hardly any front brakes.
   • Mirrors, indicator lights, the number-plate and tax disk are easy to remove and replace.
   • Vehicle Inspectorate mechanics checked each vehicle's lights, indicators, brakes, wheel nuts, steering, tyre pressure and general standard of maintenance.
   • Clumsy indicator / fog lights upset the purposeful, shark-like nose and bling-bling chrome filler cap allied with red brake callipers also look out of place.
   • Wander round to the back and the rear light clusters are designed to resemble the iris of an eye, with the sidelights, brake lights and indicators arranged in concentric circles.
   • The front light, indicators and windshield were also broken.
   • Teach your child how to spot what drivers are likely to do next, for example, the use of indicators and road signs.
   • Riders must also wear a helmet, and the scooter will need road tax, insurance, number plates, break lights, indicators and an MOT certificate.
   • CCTV footage showed the bus was stopped at a traffic stop with its indicator lights flashing.
   • However, sharp eyes will see the revised front bumper where fog lights replace the indicators, which are now housed in the main headlight fairing.
   • Most obvious changes are the new rear light assemblies - with brake, reversing and indicator lights arranged neatly within a pair of larger tail-lamp units.
   • Everything is where you want it to be, except the windscreen wipers, and indicators are on the opposite sides from where they usually are.
   • The car window was smashed, and the indicator lights were flashing.
   • The entire light cluster can be a rear light, a brake light or an indicator, and automatically adjusts in intensity and brightness to suit prevailing conditions.
   • Flashing direction indicators for motor vehicles, which will be legal in this country from Friday, were pioneered in Bradford, where they were fitted to some trolley-buses over a year ago.
   • The vehicle must also be registered with the DVLA and have lights, brakes and indicators.
2. 2.2British A board or screen in a railway station, airport, etc. giving current information.
   as modifier the indicator board

   Example sentencesExamples

   • The indicator board next to the executive officer's chair lights up like a Christmas tree.
   • There was no train anywhere near - nothing even shown on the indicator boards - and yet everyone took it with good grace, and sat patiently.
   • Back at Liverpool Street, the indicator board appeared not to be showing any platform numbers, but I found the right platform just seconds before the 18.32 pulled out.
   • The indicators which detail what stations the next train is stopping at still operate on a manual basis at Redfern station.
   • After a wait, then squeezing onto a crowded train I found myself at Liverpool Street, where the indicator board showed delayed or cancelled notices on every train.
   • Somebody was so busy looking at the train indicator in the station this morning that they walked into me and kicked my ankle.
   • Stations are being closed for renovation: indicator boards tell when the next train is due: on one line little flashing lights on a map show where the train now is.
   • The Chelmsford indicator boards were fixed by this evening, but for the last two days we've had no indicators and no announcements.

3Chemistry
A compound that changes colour at a specific pH value or in the presence of a particular substance, and can be used to monitor acidity, alkalinity, or the progress of a reaction.