Synset

being the only one; single and isolated from others
<adj.all>   (a)   (a)   (a)   (a)   (a)

lone

lonesome

only

sole

solitary

sample sentences

"the lone doctor in the entire county"
"a lonesome pine"
"an only child"
"the sole heir"
"the sole example"
"a solitary instance of cowardice"
"a solitary speck in the sky"