illicit的意思是非法的、违法的。  

New research published by the Center for Immigration Studies shows that the illicit cross-border migration in Europe – and the complementary role of asylum laws – hold learnable lessons for American land border and immigration security. 移民研究中心发布的新研究表明，欧洲的非法跨境移民以及起互补作用的庇护法为美国的边界和移民安全提供了可借鉴的经验教训。