Definition of "Alone" :
adjective: radically distinctive and without equal
"He is alone in the field of microbiology."
adjective: exclusive of anyone or anything else
"She alone believed him."
adjective: isolated from others
"Could be alone in a crowded room."
adjective: lacking companions or companionship
"He was alone when we met him."
adverb: without any others being included or involved
"The burden of proof rests on the prosecution alone."
adverb: without anybody else or anything else
"The child stayed home alone."