I would support adding the word, though it's one that many native speakers may not be familiar with.

Even though some dictionaries only list the Italian plural, the only plural I've ever seen actually used in English is cicisbeos. (I think it may have been in Georgette Heyer, lo these many years ago.) I would certainly suggest listing that as well, in case anyone comes across it in reading.

Hübsch, und mit bisher unbekannt.
Aus dem OED:
" The name formerly given in Italy to the recognized gallant or cavalier servente of a married woman.
1718 LADY M. W. MONTAGU Lett. l. II. 66 The custom of cecisbeos..I know not whether you have ever heard of those animals. 1773 Characters in Ann. Reg. 66/2 The Chichisbeo is an appendix to matrimony. 1777 SHERIDAN Sch. Scand. II. ii. 1782 WESLEY Wks. (1872) XI. 158 English ladies are not attended by their cicisbys yet; nor would any English husband suffer it. 1786 Gentl. Mag. Apr. 339/2 Link'd arm in arm, she woes her cicisbee. 1817 BYRON Beppo xxxvii, The word was formerly a ‘Cicisbeo’, But that is now grown vulgar and indecent..But ‘Cavalier Servente’ is the phrase.

2. A knot of ribbon (such as might be worn by the cavalier servente) fastened to a sword-hilt, walking-stick, etc. [So in Italian.]
a1771 SMOLLETT cited by Ogilvie."

Etymologie: 
"[It.; of uncertain origin: according to the Vocab. della Crusca, perhaps an inversion of bel cece ‘beautiful chick (pea)’; used just in the same sense. Pasqualino cited by Diez says from F. chiche beau. In mod.F. sigisbée.] "