The Collaborative International Dictionary of English v.0.48:
Apsidal \Ap"si*dal\ ([a^]p"s[i^]*dal), a. 1. (Astron.) Of or pertaining to the apsides of an orbit. [1913 Webster] 2. (Arch.) Of or pertaining to the apse of a church; as, the apsidal termination of the chancel. [1913 Webster]WordNet (r) 3.0 (2006):
apsidal adj 1: of or relating to an apse