The Collaborative International Dictionary of English v.0.48:
Oaten \Oat"en\, a. 1. Consisting of an oat straw or stem; as, an oaten pipe. --Milton. [1913 Webster] 2. Made of oatmeal; as, oaten cakes. [1913 Webster]WordNet (r) 3.0 (2006):
oaten adj 1: of or related to or derived from oats; "oaten bread"