lightship
noun
- ship that acts as a lighthouse in waters that are too deep or otherwise unsuitable for lighthouse construction
Wiktionary
noun
Etymology: From light (noun) + ship (noun). Cognate with Middle Low German lüchteschip (“lightship”), Dutch lichtschip (“lightship”).
- A ship riding at anchor and displaying a light for the guidance of sailors, in a position where a fixed lighthouse structure would be impracticable.
“Near-synonyms: lightvessel (usually synonymous), lightboat”