Complemental is a term used to describe two things that are related and work together to form a complete whole. It is often used in the context of relationships, where two people or groups are seen as COMPLEMENTARY to each other. The term can also be used to describe two objects or ideas that are related and work together to form a complete whole. The term is derived from the Latin word 'complere, ' which means 'to fill up.' The 10-letter word 'completing' and the 13-letter word 'COMPLEMENTARY' are both related to the term complemental.