enemy n. 敵人，敵軍 adj. 敵人的，敵方的
例句：After several fails the enemy was forced to retreat.
幾經失敗之后，敵軍被迫后撤。

rival n. 競爭者 對手 v. 競爭，對抗 ，相匹敵
例句：After the national selection, the party leader has been supplanted by his rival.
全民選舉之后，那位政黨領導已被他的對手取而代之了。

rivalry n. 競爭，競賽，敵對，敵對狀態
例句：Rivalry among business firms in different countries grew More intense.
不同國家的公司之間的競爭趨于激烈。

adversary n. 敵手，對手
例句：It is stupid to overestimate the strategic insight of your adversary as it is dangerous to underrate it.
過高估計你的對手的戰略遠見是愚蠢的，估計過低也是危險的。

adverse adj. 不利的，敵對的，相反的
Adverse environment forced the company to abort the development plans.
不利的環境使得公司中止了發展計劃。

opponent adj. 對立的．對抗的 n. 對手，反對者
例句：I tried to comfort Phoebe after she was defeated by her opponent in business.
菲比被她生意上的對手擊敗后，我盡力安慰她。

oppose vt. 反對，使對立，使對抗，抗爭 vi. 反對
例句：I oppose砌chard to use the office computer for the private affairs.
我反對理查德為私事使用辦公室電腦。

ally v. 結盟，同盟 n. 同盟國，支持者
例句：Britain was an ally of America in the World War I.
英國在第一次世界大戰中是美國的同盟國。

alloy n. 合金 vt. 使成合金，減低成色
例句：Aluminium alloy could be as strong as steel.
鋁合金可以和鋼強度一樣大。