coastal UK /ˈkəʊstəl/US /ˈkoʊstəl/ adjective1 •Relating to the coast; on or near the coast; longshore.These included other Niphargus species from deep cave lakes and coastal anchihaline caves [23 ] and Gammarus and Echinogammarus amphipods that live only in permanently watered streams [21 ,24 ]. — 2015 formsmore coastal · most coastal