Economic 源自 economics (經濟學) 和 economy (經濟)，意為「經濟 (上) 的，與經濟有關的；經濟學的；產生經濟效益的；有利可圖的，賺錢的」，如 Economic growth is slowing down. (經濟成長正在減緩中)；The government’s economic policies are often attacked. (政府的經濟政策常遭抨擊)；Venezuela is in the midst of an economic crisis. (委內瑞拉正處於經濟危機中)；The company had to close their Taipei office – with the rent so high it just wasn’t economic. (該公司不得不關閉台北辦事處，因為租金太高，不符經濟效益)；The airline says this route is no longer economic, so they’re going to discontinue it. (航空公司說這條航線不再賺錢，因此將予以停飛)。
Economical 亦源自 economy，意為「經濟的，省錢的，經濟實惠的，便宜的；節約的；(人) 節儉的」，如 It would be more economical to switch the machine off at night. (晚上把機器關掉會比較省錢)；an economical small car (省油的小汽車)；This laptop (computer) is very economical on electricity. (這台筆電很省電)；The material is an economical substitute for plastic or steel. (這種材料是塑膠或鋼鐵的低價替代品)；He was always economical when it came to buying presents. (談到買禮物，他總是很節儉)；Mary is an economical housewife. (瑪麗是個節儉的家庭主婦)。
從上述可知，在大多數的應用中，這兩個形容詞都不是同義詞。所以，an economic price 是對賣方有利的價格，即「有利可圖的價格；賺錢的價格」，而 an economical price 則是對買方有利的價格，即「經濟實惠的價格；便宜的價格」。然而，有些字典仍列出 economic 也有「節約的，省錢的」(= economical) 的意思，如 We must assist our clients in the most economic way. (我們必須以最省錢的方式協助我們的客戶)。同樣地，economical 有時亦被用來表示「經濟 (上) 的；經濟學的」(= economic) 的意思，如 They bought an old house for economical reasons. (基於經濟上的原因他們買了一間舊房子)。但這樣的用法畢竟少見，相信很快就會完全銷聲匿跡。
Economic 和 economical 的相反詞都是在其前加上 un-，即 uneconomic 和 uneconomical。再者，由於 economic 和 economical 的副詞都是 economically，所以 economically 兼具它們兩者的意思，意為「在經濟 (學) 上；節約地；節儉地；省錢地；便宜地」，如 economically active people (賺錢的人)；Helen dresses very economically because she makes all her clothes herself. (海倫穿著節儉，因為衣服都是她自己做的)；Economically (speaking), the country is in a very healthy state. (從經濟學的觀點來說，這國家處於非常興盛的狀態)；The project is both technically and economically feasible/viable. (這計畫無論在技術上還是在經濟上都是可行的)。顯然地，economically 是個相當常用且實用的字。