形容詞 functional:

1. designed for or capable of a particular function or use
2. involving or affecting function rather than physiology
3. relating to or based on function especially as opposed to structure
4. fit or ready for use or service
   同義詞：usable, useable, in working order, operable, operational
5. designed for or adapted to a function or use
6. (of e.g. a machine) performing or capable of performing
   同義詞：running, operative, working

1. The set of rules governing the operation of functional units of a communication system that must be followed if communication is to be achieved.
   管理某一通信系統(tǒng)的功能部件操作的一組規(guī)則，如果要實現(xiàn)通信，必須遵循這些規(guī)則。
2. The functional changes associated with or resulting from disease or injury.
   病理生理異常與疾病或傷害有關(guān)的生理變化或由其引起的生理變化
3. I'm hardly functional if I don't get eight hours' sleep!
   我要是不睡上八個小時就無法工作。

func.tion.al

adj.（形容詞）

Of or relating to a function.
職責(zé)的：有職責(zé)的或與職責(zé)有關(guān)的
Of, relating to, or indicating a mathematical function or functions.
函數(shù)的：一個或多個數(shù)學(xué)函數(shù)的、與此有關(guān)的或精于此的
Designed for or adapted to a particular function or use:
實用的：適應(yīng)某種功能或用途的：
例句：
functional architecture.
實用建筑

Capable of performing; operative:
有功能的；在起作用的：
例句：
a functional set of brakes.
性能良好的剎車系統(tǒng)

Pathology Involving functions rather than a physiological or structural cause.
【病理學(xué)】 機能的：由功能方面的原因而不是心理或構(gòu)造原因引起的

【引伸】
func.tional.ity
func.tionally
adv.（副詞）