Retard

Typically used derogatorily in context of mentally handicapped or mentally delayed people. The word Retard originally comes from the french word 'retard', which translates to 'delay' in English, which brought about the use of retarded in medical terms, such as mentally retarded. (this term is rarely used by people, and is commonly referred to as Intellectual disability, due to the negative connotation retard rings off today.)

Shorter answer: To hold back in progress, or to delay. Also used derogatorily as 'dumb' or 'idiotic'.

"The recent passing of my father may retard the progression of my history paper."