E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Domisellus.
The son of a king, prince, knight, or lord before he has entered on the order of knighthood. Also an attendant on some abbot or nobleman. The person domiciled in your house. Hence the kings body-guards were called his damoiseaux or damsels.
1
Froissart styles Richard II. le jeune damoisel Richart. Similarly Louis VII. (Le Jeune) was called the royal damsel.
2
Damoisel ou Damoiseau designait autrefois les fils de chevaliers, de barons, et toutes les jeunes gentilshommes qui netaient pas encore chevaliers. On le donnait aussi aux fils des rois qui netaient pas encore en etat de porter les armes.Bouillet: Dict. Universel.
Domisellus and domisella are diminutives of dominus, a lord. In old French we find damoiseau and damoiselle. The word Ma-demoiselle is ma domisella or damoiselle.