The Collaborative International Dictionary of English v.0.48:

Yearling \Year"ling\, n. [Year + -ling.]
   An animal one year old, or in the second year of its age; --
   applied chiefly to cattle, sheep, and horses.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Yearling \Year"ling\, a.
   Being a year old. "A yearling bullock to thy name small
   smoke." --Pope.
   [1913 Webster] yearlong

WordNet (r) 3.0 (2006):

yearling
    n 1: a young child [syn: toddler, yearling, tot,
         bambino]
    2: a racehorse considered one year old until the second Jan. 1
       following its birth
    3: an animal in its second year