The charity event was unpublicized, so very few people attended.

unpublicized 是由前缀 un-（表示"不、未"）和动词 publicize（"宣传、公布"）的过去分词 publicized 组合而成。publicize 本身来自名词 public（"公众"）加上动词后缀 -ize（"使...化"）。unpublicized 整体意思是"未经宣传的"。