The Collaborative International Dictionary of English v.0.48:

Subaxillary \Sub*ax"il*la*ry\, a.
   1. (Anat.) Situated under the axilla, or armpit.
      [1913 Webster]

   2. (Bot.) Placed under the axil, or angle formed by the
      branch of a plant with the stem, or a leaf with the
      branch.
      [1913 Webster]