noun

1. 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. A scalar-valued linear function on a vector space.

3. An object encapsulating a function pointer (or equivalent).

adjective

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”

Synonyms: functioning, working, utilitarian