The Collaborative International Dictionary of English v.0.48:

Discoidal \Dis*coid"al\, a. [Cf. F. disco["i]dal.]
   Disk-shaped; discoid.
   [1913 Webster]

WordNet (r) 3.0 (2006):

discoidal
    adj 1: having a flat circular shape [syn: discoid,
           discoidal, disklike, disclike, disk-shaped,
           disc-shaped]