a first [full, own] cousin (第一代)嫡堂[表]兄[弟、姊、妹]
a second cousin (第二代)嫡堂[表]兄[弟、姊、妹]之子(或女);【俚】隔房堂[表]兄弟(或姊妹)(first cousin once removed)
a third cousin (第三代)嫡堂[表]兄[弟、姊、妹]之孙(或孙女);【俚】隔房堂[表]兄弟姊妹之子(或女)(first cousin twice removed).