Polygenic

A disease or trait that is described as being polygenic involves alleles of two or more genes - 'poly' coming from the Greek 'polus' meaning 'much' or 'polloi', meaning 'many'.

A polygenic trait is a phenotype which is affected by multiple gene loci, for example height or eye colour.  However, traits such as height can also be affected by environment, therefore they are described as multifactorial.

1.  http://ghr.nlm.nih.gov/glossary=polygenic

2. Hartl, D and Ruvolo M, (2012) Genetics, Analysis of Genes and Genomes, Eighth Edition, Jones and Bartlett Learning, p663; 765