Where does “λόγγος” come from?

λόγγος (Greek) comes from Byzantine Greek λόγγος, from Proto-Slavic lǫgъ, from Proto-Balto-Slavic lanˀgas, from Proto-Indo-European lengʷʰ- — light, agile, nimble; light, not heavy, agile,...

λόγγος (Greek): dense and bushy forest, grove