學習英語的人常常會遇到這樣的問題：有些單詞很奇怪，當你正確地選用了它們時，同時你又會懷疑是不是錯選了。因為這些詞有著完全不同甚至相反的意思。

自反義詞（contronym，也叫contranym or autoantonym）是一個具有兩種含義的詞，而且這兩種含義恰好相反。語法上說，“自反義詞是同音詞（是另一個拼寫相同但含義不同的詞），也是反義詞（意思相反的詞）。”

但一些嚴謹的語法學家認為，從專業角度講，它們是同形異義詞（homographs）。同形同音異義詞（homonyms）發音相同；如果發音不同，則為同形異音異義詞（heteronyms）。

自反義詞有時也被稱為“Janus詞”，“Janus”是羅馬神話中的兩面神的名字。下面我們列舉30個英語中常見的自反義詞。

1.Bolt

To separate by fleeing or to hold together (as with a bolt)

2.Bound

Going toward a destination or restrained from moving

3.Buckle

To fasten together (with a buckle) or to bend or collapse from pressure

4.Cleave

To adhere firmly and closely or to split apart

5.Clip

To fasten (as with a paperclip) or to detach with shears (clipping your hair or your hedges)

6.Consult

To give advice or to get advice

7.Custom

A common practice or a specially made item

8.Dust

To cover something with a fine power or to make something clean by brushing or removing dust

9.Enjoin

To order someone to do something or to prohibit someone from doing something

10.Fast

Firmly fixed and unmoving or able to move rapidly

11.Finished

Completed or destroyed

12.Garnish

To add decorative touches (to food or drink) or to take/withhold from (as in wages)

13.Handicap

An advantage given to equalize chances of winning (as in golf) or a disadvantage that makes equality difficult

14.Lease

To rent property or to offer property for rent

15.Left

Departed or remained behind

16.Model

The original, perfect example or a copy

17.Off

Not operating (turn off the light) or operating (the alarm went off)

18.Out

Visible (the stars are out) or invisible (the lights are out)

19.Overlook

To watch or to fail to notice

20.Oversight

Watchful, responsible care or a mistake made due to forgetfulness or poor supervision

21.Peruse

To skim or to read very carefully

22.Ravel

To separate or to become entangled

23.Rent

To lease something or to offer an something for lease

24.Sanction

To boycott or to approve

25.Screen

To hide or to show (like a movie)

26.Seed

To add seed (seeding the lawn) or to remove seed (seeding a watermelon)

27.Strike

To hit or to miss while trying to hit

28.Trim

To add (decorations) or to take away (extra hair or fabric, for example)

29.Wear

To endure or to deteriorate

30.Weather

To withstand or to be worn away