One way to have a half cousin is, as in my husbands family in Wales, where the grandmother married for a second time. The children of each half sibling were half cousins to each other. In his case complicated to three quarter cousins, perhaps, as the grandmothers two husbands were full cousins to each other and had the same surname. Just a thought. Or could it be an adopted child who was always refered to as a half cousin as she or he were not really fully related? One of my aunts insisted her child was adopted, aquired during the war, all those poor motherless children! The family never fully believed her but that cousin was always added to the list as an afterthought. A conversation might go - There are 11 cousins, Oh, and ........ of course. Tina