functional

Etymology

function +‎ -al

Adjective

functional (comparative more functional, superlative most functional)

1. In good working order.
2. Useful; serving a purpose, fulfilling a function

   That sculpture is not merely artistic, but also functional: it can be used as a hatrack.

3. Only for functional purposes, notably in architecture

   A functional construction element generally must meet higher technical but lower aesthetical requirements

4. (computing theory) Having semantics defined purely in terms of mathematical functions, without side-effects.
5. (medicine) Of a disease, such that its symptoms cannot be referred to any appreciable lesion or change of structure; opposed to organic disease, in which the organ itself is affected.

Noun

functional (plural functionals)

1. (mathematics) A function that takes a function as its argument; More precisely: A function y=f(x) whose argument x varies in a space of (real valued, complex valued) functions and whose value belongs to a monodimensional space. An example: the definite integration of integrable real functions in a real interval.
2. (mathematics, functional analysis) A scalar-valued linear function on a vector space.
3. (computing) An object encapsulating a function pointer (or equivalent).

References

• functional on Wikipedia.Wikipedia

Further reading

• functional in Webster’s Revised Unabridged Dictionary, G. & C. Merriam, 1913
• functional in The Century Dictionary, The Century Co., New York, 1911
• functional at OneLook Dictionary Search