feeler
A body part or action used to carefully test something.
A feeler is something used to explore or test a situation carefully before fully committing.
When a crab uses its long antennae to touch and sense what's around it in the dark water, those antennae are called feelers. Insects have feelers too: a butterfly gently taps flower petals with its feelers to find nectar, and an ant waves its feelers to communicate with other ants and navigate its path.
People use the word in a similar way when they're being cautious about something new or uncertain. If you want to know whether your friends would be interested in playing a new game at recess, you might put out feelers by casually mentioning it to see their reaction. If your dad is considering a job in a new city, he might send out feelers by calling contacts there to learn about opportunities, without actually applying yet. A business might put out feelers to gauge customer interest in a possible new product.
Using feelers means you're gathering information before making a decision, just like that crab touching its surroundings before moving forward. It's a smart way to avoid diving in blindly when you're not sure what to expect.