We don't have synonyms for demi-lune yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are demilune, demi lune and semilune.
(n) :
Alternative form of demilune. [(military, architecture) A fortification constructed beyond the main ditch of a fortress, and in front of the curtain between two bastions, intended to defend the curtain; a ravelin.]
(n) :
Alternative form of demilune. [(military, architecture) A fortification constructed beyond the main ditch of a fortress, and in front of the curtain between two bastions, intended to defend the curtain; a ravelin.]