An antigen of the Rhesus system; understood unless otherwise specified to refer to Rhesus factor D (RhD), which appears on the surface of the red blood cells of most (85%) humans. An incompatibility between the Rh-blood types of a mother and her baby may cause serious disease for the baby.

(idiomatic) An unknown or hard-to-define influence; a factor with unknown or unforeseeable consequences. / (idiomatic) A special talent, ability or quality or its indefinable cause.

Alternative spelling of X factor

Alternative spelling of X factor

Alternative spelling of X factor

plural of factoid

(mathematics) The decomposition of a composite number into a product of smaller integers

(informal, US) A film studio

(mathematics) Capable of being factored. For integers synonyms are composite, non-prime.

Alternative spelling of factorizable