1.
Functional things are useful rather than decorative.
...modern, ~ furniture...
The decor is ~.
ADJ
2.
Functional means relating to the way in which something works or operates, or relating to how useful it is.
...rules defining the territorial boundaries and ~ limits of the local state.
ADJ: ADJ n
3.
Functional equipment works or operates in the way that it is supposed to.
We have fully ~ smoke alarms on all staircases.
= operational
ADJ