WordNet sense 1 (an enlisted man of the lowest rank):

buck private, common soldier

WordNet sense 2 (concerning one person exclusively):

individual

WordNet sense 3 (concerning or affecting a particular person or his or her private life and personality):

personal

WordNet sense 4 (hidden from general view or use):

privy, secluded, secret

WordNet sense 5 (not invested with or related to prominent position or status etc.):

nonpublic

WordNet sense 6 (entrusted with private information and the confidence of another):

confidential