type of fish with a head formed to attach to objects or other fish," 1560s, from Latin remora "sucking fish," literally "delay, hindrance," from re- "back" (see re-) + mora "delay" (see moratorium); so called because the fish were believed by the ancients to have the power to retard a vessel to which they attached themselves.
Hence, in 17c.-18c., "an obstacle, an impediment" (the first sense of the word in Johnson's dictionary). The belief seems to predate the Romans: in Greek, such fishes were ekhenēis, literally "ship-holder," from ekhein "to hold" + naus (dative nei) "ship." Pliny writes that Antony's galley was delayed by one at Actium, and popular fables of the fish and its power to hold in place ships under sail circulated widely in the Middle Ages and after, from Ovid, etc. Sometimes called in English stayship or stopship.