A dictionary of Confusable Phrases: More Than 10,000 Idioms and Collocations

open sea • open water
open sea —
1
. the part of the sea not closed in by land (not
a bay or harbor): A “black south-easter,” the wind most feared
on this coast, forced most of the fleet to run for open sea. 2.
the part of the sea outside the territorial jurisdiction of any
country: The real place of meeting between the Englishman
and the Spaniard was on the open sea. 3. sea that is practically
free from ice and navigable: It is probable that an open sea
stretches to the Antarctic pole.
open water — = open sea 3: Von Wrangell found open
water — or what is now often called a “Polynia,” an open sea.
open to someone • open with someone
open to someone —(of a shop, restaurant, etc.) accessible to
people who may come: The library is not open to the public
this week.
open with someone —willing to honestly and frankly talk
about things with another person: Parents should try to be
open with their children.
open town • wide-open town
open town —
1
. (U.S.) a town characterized by a lack of
restrictions on places for drinking, gambling, etc.: They form
a Committee to clean up San Francisco, and as chairman they
take the man who’s been running it as an open town for sixteen
years. 2. an undefended town exempt from enemy bombard-
ment because of its great historical importance: It may mean
surrender in return for such quite valueless concessions as “no
bombing of open towns.”
wide-open town — = open town 
1
: He has been elected three
times because the citizens want a wide-open town.
open up on someone • open up to someone
open up on someone —
1
. start shooting at a person: Just as
we reached that spot a group of soldiers opened up on us with
rockets, automatic rifles, and grenades. 2. subject a person to
a harsh verbal assault or criticism: When we’d killed most of
a bottle of wine discussing the literary projects, she opened
up on me.
open up to someone —
1
. (also: open up with someone) talk to
smb. frankly or intimately: Although he never answered — or
perhaps because of it — I opened up to him completely, telling
him things I’d never told anyone. 2. become more accepting
of a person: I stayed during the breaktime, so a few of the
boys stayed also. They finally opened up to me especially the
quiet ones.