名詞 operative:

1. a person secretly employed in espionage for a government
   同義詞：secret agent, intelligence officer, intelligence agent
2. someone who can be employed as a detective to collect information
   同義詞：private detective, PI, private eye, private investigator, shamus, sherlock

形容詞 operative:

1. being in force or having or exerting force
2. of or relating to a surgical operation
3. relating to or requiring or amenable to treatment by surgery especially as opposed to medicine
   同義詞：surgical
4. effective; producing a desired effect
   同義詞：key
5. (of e.g. a machine) performing or capable of performing
   同義詞：running, functional, working

1. This law becomes operative on 12 May.
   此法令自5月12日起生效。
2. The boss is hopping mad about it and `mad' is the operative word.
   老板對此事暴跳如雷--｀暴跳如雷＇這個成語在句中最重要。
3. The oil rig is now fully operative.
   石油鉆塔現(xiàn)全面開工。
4. The station will be operative again in January.
   該車站將於一月份恢復使用。

op.er.a.tive

adj.（形容詞）
Being in effect; having force; operating:
有效的；有力量的；行動的：
例句：
.Two major tendencies are operative in the American political system.(Heinz Eulau)
.在美國的政治體系中以兩種主要潮流為主.(海因茨·奧勞)

Functioning effectively; efficient.
有效運用的，有效率的
Engaged in or concerned with physical or mechanical activity.
與體能有關的，或機械活動有關的
Of, relating to, or resulting from a surgical operation.
手術的：外科手術的，與外科手術有關的，由外科手術引起的
n.（名詞）
A skilled worker, especially in industry.
熟練工人：熟練工人，尤指工廠技工

A secret agent; a spy.
特務，間諜
A private detective.
私人偵探

【引伸】
op.eratively
adv.（副詞）