official

officer, official

这两个名词均含“官员”之意。
officer: 主要指军官或警官，有时也指文职官员或高级职员。
official: 通常指文职官员，公职人员，有时也指军官或警官。

名词 official:

1. a worker who holds or is invested with an office
   同义词：functionary
2. someone who administers the rules of a game or sport

形容词 official:

1. having official authority or sanction
2. of or relating to an office
3. verified officially
4. conforming to set usage, procedure, or discipline
   同义词：prescribed
5. (of a church) given official status as a national or state institution

1. The protesters showed their defiance of the official ban on demonstrations.
   抗议者藐视官方的示威禁令。
2. He is a pompous official.
   他是个自命不凡的官员。
3. I happen to have the official statistics with me.
   我碰巧身边有官方的统计数字。
4. The mayor is a considerable official.
   市长是一位重要的官员。
5. The group have split away/off from the official union.
   这一部分人已从正式的联盟中分裂出来了。
6. They expressed their dissent from official policy.
   他们对官方的政策表示出异议。
7. She received several official letters this morning.
   她今天早晨收到了几封公函。
8. An official of the local government called to see him.
   当地政府一位官员来看他。

of.fi.cial

adj.Abbr. off.（形容词）缩写 off.
Of or relating to an office or a post of authority:
职务上的：与职务或权力职位有关的：
例句：
official duties.
公务

Authorized by a proper authority; authoritative:
有权威的：由适当权力机构授于的：
例句：
official permission.
正式批准

Holding office or serving in a public capacity:
供职的：供职或在公共职能部门中服务：
例句：
an official representative.
一个官方的代表

Characteristic of or befitting a person of authority; formal:
正式：以权威人物为主的或适合权于威人物的；正式：
例句：
an official banquet.
一次正式宴会

Authorized by or contained in the U.S. Pharmacopoeia or National Formulary. Used of drugs.
（药）法定的：美国的药书或药典授权的或含有的。用于药物
n.Abbr. off.（名词）缩写 off.
One who holds an office or a position, especially one who acts in a subordinate capacity for an institution such as a corporation or governmental agency.
公务员，职员：一个供职的人，尤指在如公司或政府机构的下属机构工作的人
Sports A referee or an umpire.
【体育运动】 裁判

来源：
From Middle English [ecclesiastical officer]
源自 中古英语 [教会的人员]
from Old French
源自 古法语
from Latin offici3lis [an attendant of an office]
源自 拉丁语 offici3lis [办公室的服务人员]
from officium [duty, service] * see office
源自 officium [责任，服务] *参见 office

【引伸】
offi.cialdom
n.（名词）
offi.cially
adv.（副词）