Physically they were humanoids with a complex bone structure around the top of their noses. They had premaxilla bones. Their world depended on trade with alien species. There were strict protocols about those relations, and even being accused of violating them was a serious offense. In fact, even an accusation of wrongdoing could end the career of an Entharan trader.
Technology available to this species included Monofilament stimulators, Electro-dynamic probes, Micro-calipers, dermal regenerators, and transporters, and weapons such as Isokinetic cannons and a thoron rifles describes as crude, but effective.
They were familiar with the Borg.
USS Voyager visited an Entharan colony in 2374. There, the crew attempted to trade with Kovin, a weapons trader. Unfortunately, an accident during a demonstration led Seven of Nine to wrongfully accuse the trader of mistreating her. Sadly, Kovin was killed before the mistake could be rectified. (VOY: "Retrospect")