aloneYou can tell me your secret - I think we're alone.
(all) on your ownI like living on my own.
on your lonesomeUKinformalSure, you can play the game on your lonesome, but it's more fun with friends.
on your todUKold-fashionedinformalAh, your family's gone and left you on your tod, have they?
unaccompaniedTo everyone's great surprise, she arrived at the ball unaccompanied.
solitaryHe was a solitary child who preferred reading a book to football.
reclusiveThe author is notoriously reclusive and avoids the spotlight.
seclusiveformalShe was seclusive and avoided society.
isolatedThere were isolated cases of the disease, but no widespread outbreak.