from private (adj.) + abstract noun suffix -cy
1590s, "a private matter, a secret;"
Earlier was privatie from Old French privauté.
late 14c. as "secret, mystery;"
c. 1400 as "a secret, secret deed; solitude, privacy"
c. 1600 as "seclusion,"
beginning 1814, "state of freedom from intrusion"
"pertaining or belonging to oneself, not shared, individual; not open to the public"
of a religious rule, "not shared by Christians generally, distinctive"
from Latin privatus "set apart, belonging to oneself (not to the state), peculiar, personal"
used in contrast to publicus, communis
past participle of privare "to separate, deprive"
from privus "one's own, individual,"
from Proto-Italic *prei-wo- "separate, individual"
from PIE *prai-, *prei- "in front of, before"
from root *per- (1) "forward"
The semantic shift would be from "being in front" to "being separate."
Old English in this sense had syndrig.
Private grew popular 17c. as an alternative to common (adj.), which had overtones of condescension.
Of persons, "not holding public office," recorded from early 15c.
In private "privily" is from 1580s. Related: Privately.
private school from 1650s
private property by 1680s
private parts "the pudenda" from 1785
private enterprise first recorded 1797
private eye "private detective" recorded from 1938, American English.
private sector, private sectoris from 1948
1590s, "private citizen"
short for private person "individual not involved in government" (early 15c.)
from Latin privatus "man in private life," noun use of the adjective
1781 in the military sense
short for Private soldier "one below the rank of a non-commissioned officer" (1570s)
from private (adj.).
-- adapted from: Online Etymology Dictionary