ilex Syllabification: (i·lex)Pronunciation: /ˈīˌleks/Definition of ilex noun 1another term for holm oak. 2a tree or shrub of a genus that includes holly and its relatives. Genus Ilex, family Aquifoliaceae Origin: late Middle English: from Latin, 'holm oak'ilex in other Oxford dictionaries Definition of ilex in the British & World English dictionary