這兩個拼字相近的形容詞，意思並不相同。defensible 意為「(見解，主張、看法等) 可辯護的，站得住腳的；(地方) 能防禦的，能保衛的」，如 Although opinions differ on this matter, mine is defensible. (雖然對這件事各人的看法不一，但我的看法是站得住腳的)；His behavior was perfectly defensible. (他的行為是完全可以辯解的)；This is a defensible fortress/position. (這是個能防禦的堡壘/位置)。這個字的反義詞為 indefensible。
Defensive 意為「防衛性的，防衛用的；(人或行為) 防衛的，守勢的，自衛的；(比賽中) 防守的」，如 The United States has decided to sell more defensive weapons to Taiwan. (美國已決定出售更多防衛性武器給台灣)；The rebels adopted defensive tactics temporarily. (叛軍暫時採取防衛性戰術)；She became very defensive when I asked her how much the car had cost. (當我問她這輛車多少錢時，她便充滿戒心，不願多談)；They made a strong defensive effort in the second half of the game. (他們下半場頑強地防守)。defensive 還可當名詞用，但僅用在 be on the defensive (採取守勢)、put sb on the defensive (使某人處於守勢) 等片語中，如 The scandal has put the school’s leadership on the defensive. (這項醜聞已使學校領導階層處於守勢)。
就「防衛性的，防衛用的；防守的」意思而言，defensive 的反義詞為 offensive，意為「攻擊性的；(比賽中) 進攻的」，如 The United States provided the Iraqi army with offensive weapons. (美國提供伊拉克軍隊攻擊性武器)；They are offensive players. (他們是進攻型球員)。從上述可知，互為相反詞的 defensive 和 offensive 僅用於名詞前。同樣地，offensive 亦可當名詞用，但僅用在 be on the offensive (採取攻勢)、go on the offensive 或 take the offensive (率先攻擊，先發制人) 等片語中。