c. 1600, "solitary, lone; unfrequented," from lone + -ly (1). Meaning "dejected for want of company" is from 1811. Lonely heart (n.) "a lonely-hearted person" is from 1922. Lonely hearted (adj.) is attested from 1820.
a lonely existence
a lonely soul
a lonely fisherman stood on a tuft of gravel
the loneliest night of the week
felt sad and lonely
a lonely crossroads