In anatomy, pertaining to the axilla; contained in the axilla: as, the axillary boundaries; the axillary vessels.In the arthropod animals, pertaining to an articulation or joint: said of parts which are attached to the point of union of two joints or other movable parts of the body.In botany, pertaining to or growing from the axil (of plants). See cut under axil.n. Same as axillar.n. In the Crinoidea, the pentagonal plate which supports the branched arms.