Monosomy is a medical term that refers to a genetic condition in which a person has only one copy of a chromosome instead of two. This condition can result in physical and developmental abnormalities. Synonyms for monosomy include haploidy, which is a condition in which a cell or organism has only one set of chromosomes; monoploidy, which is a condition in which an organism has only one set of chromosomes instead of the usual two; and chromosomal deletion, which refers to the loss of a chromosome segment. Other terms used to describe monosomy include partial monosomy, which refers to the loss of part of a chromosome, and complete monosomy, which refers to the loss of an entire chromosome.