1. Without any others being included or involved
   "the burden of proof rests on the prosecution alone";
   - entirely, exclusively, solely, only, purely
    
2. Without anybody else or anything else
   "the child stayed home alone"; "the pillar stood alone, supporting nothing";
   - solo, unaccompanied

1. Isolated from others
   "I want to be alone"; "could be alone in a crowded room"; "was alone with her thoughts"
    
2. Lacking companions or companionship
   "he was alone when we met him"; "she is alone much of the time";
   - lone, lonely, solitary
    
3. Exclusive of anyone or anything else
   "she alone believed him"; "cannot live by bread alone";
   - only
    
4. Radically distinctive and without equal
   "he is alone in the field of microbiology"; "this theory is altogether alone in its penetration of the problem";
   - unique, unequaled [US], unequalled [Brit, Cdn], unparalleled, one-of-a-kind

See also: exclusive, incomparable, unaccompanied, unambiguously, uncomparable, uniquely, unsocial

Encyclopedia: Alone, Part 3