syndactyly
noun
syn·dac·ty·ly (ˌ)sin-ˈdak-tə-lē 
: a union of two or more digits that is normal in some animals (such as various marsupials) and that in humans occurs as an inherited condition or as a part of several genetic disorders and is marked by webbing of two or more fingers or toes and sometimes bony fusion of adjacent digits
Example Sentences
Recent Examples on the Web The same may be true of developmental disorders — like syndactyly. 
Natalie Angier, New York Times, 9 Jan. 2017
Natalie Angier, New York Times, 9 Jan. 2017 Word History
Etymology
New Latin syndactylia, from syn- + Greek daktylos finger
First Known Use
1864, in the meaning defined above
Medical Definition
syndactyly
noun
syn·dac·ty·ly -lē
plural syndactylies
: a union of two or more digits that is normal in some animals and that in humans occurs as an inherited condition or as a part of several genetic disorders and is marked by webbing of two or more fingers or toes and sometimes bony fusion of adjacent digits