Alone, and on your own / by yourself (which are less formal and are the normal phrases used in spoken English), describe a person or thing that is separate from others. They do not mean that the person is unhappy. * alone 和较非正式、常用于口语的 on your own、by yourself 均指独自，但无孤独之义：◆I like being alone in the house.我喜欢独自一人待在家里。◆I'm going to London by myself next week.我准备下星期一个人去伦敦。◆I want to finish this on my own(= without anyone's help).我想独自完成这项工作。
Lone/solitary/single mean that there is only one person or thing there; lone and solitary may sometimes suggest that the speaker thinks the person involved is lonely. * lone、solitary、single 意为单独；lone 和 solitary 有时可能暗示说话者认为谈及的人孤单：◆a lone jogger in the park在公园里独自慢跑的一个人◆long, solitary walks独自一人长途行走
Lonely (NAmEalsolonesome) means that you are alone and sad. * lonely（美式英语亦作 lonesome）意为孤寂：◆a lonely child孤寂的孩子◆Sam was very lonely when he first moved to New York.萨姆刚搬到纽约时非常寂寞。It can also describe places or activities that make you feel lonely. * lonely 还可描述使人感到孤寂的地方或活动：◆a lonely house一座冷清的房子