Sanskrit asura.  In Buddhism, asura are generally considered evil and fearsome spirits fond of fighting, but some of them are good and protect Buddhism. Often abbreviated as 修羅. One of the six kinds of rebirth 六道.

六道之一，華譯為非天，因其有天之福而無天之德，似天而非天。又譯作無端，因其容貌很醜陋。又譯作無酒，言其國釀酒不成。性好鬥，常與帝釋戰，國中男醜女美，宮殿在須彌山北，大海之下。

陳義孝編, 竺摩法師鑑定, 《佛學常見辭彙》

asura, 修羅 originally meaning a spirit, spirits, or even the gods, it generally indicates titanic demons, enemies of the gods, with whom, especially Indra, they wage constant war. They are defined as 'not devas', and 'ugly', and 'without wine'. Other forms are 阿須羅 (or 阿蘇羅, or 阿素羅); 阿修倫 (or羅須倫 or 阿修輪 or 羅須輪); 阿素洛; 阿差. Four classes are named according to their manner of rebirth-egg, born, womb-born, transformation-born, and spawn- or water-born. Their abode is in the ocean, north of Sumeru, but certain of the weaker dwell in a western mountain cave. They have realms, rulers, and palaces, as have the devas. The 阿修羅道 is one of the six gatis, or ways of reincarnation. The 修羅場 or 修羅巷 is the battlefield of the asuras against Indra. The 阿修羅琴 are their harps.

A Dictionary of Chinese Buddhist Terms, William Edward Soothill and Lewis Hodous

梵名 Asura。略稱修羅。為六道之一，八部眾之一，十界之一。又作阿須羅、阿索羅、阿蘇羅、阿素羅、阿素洛、阿須倫、阿須輪。意譯為非天、非同類、不端正。舊譯不酒、不飲酒，或係誤譯。阿修羅為印度最古諸神之一，係屬於戰鬥一類之鬼神，經常被視為惡神，而與帝釋天（因陀羅神）爭鬥不休，以致出現了修羅場、修羅戰等名詞。
據增一阿含經卷三阿須倫品載，其身形廣長八萬四千由旬，口縱廣千由旬。另於長阿含經卷二十阿須倫品、大樓炭經卷二阿須倫品、起世因本經卷五，均詳載其住處與事蹟。有關阿修羅之業因，諸經多舉出瞋、慢、疑等三種生因，佛為首迦長者說業報差別經則列舉十種阿修羅之生因：(一)身行微惡，(二)口行微惡，(三)意行微惡，(四)起憍慢，(五)起我慢，(六)起增上慢，(七)起大慢，(八)起邪慢，(九)起慢慢，(十)迴諸善根。此外，阿修羅所持有之琴，特稱為阿修羅琴。阿修羅欲聽聞何種曲調，則曲音自然彈出。此亦阿修羅所具有之褔德。
阿修羅之形像有多種說法，或謂九頭千眼，口中出火，九百九十手，六足，身形為須彌山之四倍；或謂千頭二千手、萬頭二萬手、三頭六手；或謂三面青黑色，忿怒祼形相，六臂。〔長阿含經卷十、卷二十一、大智度論卷十、卷十一、卷三十、佛地經論卷六、觀音經義疏記卷四、法華經文句卷二、慧苑音義卷上、翻譯名義集卷二〕

佛光電子大辭典

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六道（六趣）眾生之一，另作「阿修羅道」，此處有情生性猜疑、好戰，常與忉利天（三十三天）眾征戰，各有勝負。另譯為「阿須倫」，意譯為「非天、不端正、非善戲、非同類」，簡稱為「修羅」。

漢譯阿含經辭典，莊春江編(1.4版)

Asura  阿修羅  It is a peculiar path in the Six Paths. In terms of material enjoyment and psychic power, it is similar to Deva. However, in some aspects, it is even worse than Human Path. The male Asura is extremely ugly and furious, and always fight with each other. The female Asura is as beautiful as an angel. They are proud of themselves, thus reluctant to learn and practice Buddhism.

漢英-英漢-英英佛學辭典字庫