A complementizer is a °marker that indicates that the °clause on which it occurs is a °complement clause.
Note that there is no corresponding verb ("to complementize").
complementizer (STR) = a morpheme that overtly expresses the semantic relation in a complement clause construction. Example: in She thought that he was tired, that is the complementizer. A complement clause construction with a complementizer is an example of syndetic subordination. If the morpheme is affixed to a predicate, it is not a complementizer but an overt marker of deranked status. (Section 18.3.1)