Its source is hros lind, an Ancient Germanic name meaning "Gentle horse."
Poet Edmund Spenser (1552-1599) believed that he invented this name for The Shepheardes Calendar as a means of hiding the identity of the object of the affection expressed in the poem. It was a fairly transparent device, Rosalind being a simple anagram of selected letters from the woman's real name, Rosa Daniel.
The name was picked up by Thomas Lodge for the title character of his 1599 novel Rosalynde. Both name and story were seized upon by William Shakespeare for his play As You Like It, written shortly after Lodge's novel appeared.
Even if the Normans used the name centuries before, it was this trio of Elizabethan writers who handed it down to us rich with poetic associations.