字首un：
successful – unsuccessful.
reliable – unreliable.
shaven – unshaven.
important – unimportant.
predictable – unpredictable.
comfortable-uncomfortable.
fortunate-unfortunate.
finished-unfinished.（未完成的.）
doubted-undoubted.（無疑的）
unemployment-unemployment.（失業）
able-unable.
believable-unbelievable.
comfortable-uncomfortable.
abashed-unabashed.（不害羞的）
accessible-unaccessible.（難親近的）
accountable-unaccountable.（不能說明的）
adjusted-unadjusted.（未調整的）
affiliated-unaffiliated.（非附屬的）
healthy-unhealthy.（不健康的）