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
