Noun
A hare in the first year of its age.
Source: Webster's dictionaryA pasty costly made, Where quail and pigeon, lark and leveret lay, Like fossils of the rock, with golden yolks; Imbedded and injellied. Alfred, Lord Tennyson
A hare less than one year old is called a leveret. Source: Internet
A young hare is called a leveret; this term is sometimes informally applied to a young rabbit as well. Source: Internet