Of or pertaining to something at its lowest point; designating the part opposite to the apex. [https://books.google.com/books?id=aW0zkZl0JgQC&lpg=RA1-PA2&dq=abapical&pg=RA1-PA2#v=onepage&q=abapical&f=false Mosby's Medical Dictionary, 9th edition], via Google Books.