同族词既然是由同一词根派生而成，它们之间便有“血脉”关系，而且在词义上，也常有相似之处。
学习英语词汇时，可以利用同族词这特色把每组词集中起来，用对比方式，辨别每个词的词义和不同用法，然后加以记忆和运用，假以时日，不难水到渠成，词汇丰富。
下面便是两组同族词的意思及其用法：
Ⅰauthorise（动词）授权、批准
authorisation（名词）授权、委任
authoritative（形容词）权威的、命令式的
authority（名词）权力、职权、权威
authorities（名词）当局
① Dr Li has authorised David to act for him in his absence.
② The Ministry for Finance authorised the payment of annual increments.
③ One needs special authorisation to enter such a building.
④ This news came from an authoritative source, so it must be reliable.
⑤ The Commander-in-chief spoke in an authoritative tone.
⑥ As a senior officer, Jason is entitled to have authority over the clerical staff.
⑦ Who gave you authority to implement the new salary scheme?
⑧ Dr Wong is an authority on language teaching.
⑨ The authorities concerned must see to it that the same thing will not recur.
Ⅱclear（形容词）清楚的、明白的、无嫌疑的、债务已清的；
（副词）远离的
（动词）清除、解除。
clearance（名词）清除、许可（证）
（修饰语）清货
clearing （名词）林中空旷的
clearly（副词）清楚地
① The speaker's voice is clear enough to be heard.
② Can you make your last point clearer?
③ The suspect was clear of suspicion.
④ The gambler hopes to be clear of debts soon.
⑤ Unauthorised persons are advised to keep clear of the premises.
⑥ The police have cleared the road of obstruction.
⑦ If there exists misunderstanding among friends, please clear it up.
⑧ Have you seen any slum clearance?
⑨ The plane must get clearance for take-off.
⑩ Before Christmas, shopping centres have the habit of holding annual clearance sales.
11. The picnickers pitched their camp in the clearing.
12. Speak clearly or the audience at the back may not be able to hear you.
