Entry 1 sense Webster, 1913 Endothelial /ĕnˌ-dōth-ēl'-ēˌ-əl/ · En·do·the·li·al · IPA /ˌɛndoʊθˈiːlˌiːəl/ 01 a. Of, or relating to, endothelium. 1. Of, or relating to, endothelium.(Anat.)