Definition of affine in US English:

affine

Mathematics
• Allowing for or preserving parallel relationships.

• ‘Our interest is in the space of affine equivalence classes of equal-area polygons.’
• ‘It can be obtained from the previous description by applying affine transformations to keep the polygon bounded as it degenerates.’
• ‘The simplest way to see why this assertion is true is to observe that any triangle in the plane can be mapped by an invertible affine transformation to an equilateral triangle.’
• ‘Still to be implemented are geometric primitives and affine transformation of images.’
• ‘Using parallelograms to define affine transformations may be a mixed blessing.’

noun

Anthropology
• A relative by marriage.

• ‘Finally the ‘deceased wife's sister’ law was belatedly reformed in 1906, although marriage between such affines as adoptive parents and children, and adoptive siblings, remained within the prohibited degrees.’
• ‘In addition to kins and affines, almost all the villagers are invited to join in.’
• ‘That group includes affines, based upon the theological idea that as husband and wife were one, marriage to a sister-in-law was as incestuous as marriage to a sister.’
• ‘They were sisters, mothers, daughters, affines, rather than simply women in groups.’
• ‘When a dying person breathes his/her last breath, close relatives, normally affines, wash and put new clothes on the body.’

Origin

Early 16th century (as a noun): from Old French afin or Latin affinis ‘related’ (see affinity). The mathematical sense dates from the early 20th century.

/əˈfīn/