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

half-hourly • on the half hour
half-hourly —done or occurring every half hour: We’ll be
running more trains, with half-hourly departures to Paris and
hourly departures to Brussels.
on the half hour —occurring exactly thirty minutes after an
hour marked on a clock: The clock should chime once on the
half hour and twice on the hour.
half one (two, etc.) • half past one (two, etc.)
half one (two, etc.)—(UK coll.) thirty minutes after one (two,
etc.) o’clock: Instead of arriving at half one in Cape Town, I
was only there at half four.
half past one (two, etc.)—a commonly used variant of the
former: At twenty past twelve we arrived at Farmers Bridge
Locks, which we completed by half past one.
half-seas over • overseas
half-seas over —(UK coll.) drunk: I learned later that Charley
had run across an old college pal, and was half-seas over in a
bar up one street.
overseas —across or beyond a sea, especially in another coun-
try: The country is up in arms over the denial of voting rights
to the men serving overseas.
half the time • half time
half the time —(hyperbolic) 
1
. a much shorter time than is
normal or expected: I could have done it in half the time. 2.
a considerable time: I’m not surprised he didn’t complete the
exam — he spent half the time looking out the window. 3.
habitually; very frequently: She calls on the neighbors, she’s
out half the time and doesn’t answer the telephone.
half time —
1
. an interval between the two halves of a game
of football, hockey, etc.: Before half-time he kicked two goals
out of the three registered for Middlesex. 2. half the time usu-
ally worked: I worked halftime in the atmospheric sciences
department with a professor I consider a genius.
half the world • half-world
half the world —is used to hyperbolically designate a great
quantity or number: Half the world buys British when it
comes to cars, especially semi-sports jobs like this.
half-world— a social group considered to be not wholly
respectable: Away from his chosen half-world, Munby’s social
life was passed in the first literary and artistic circles of his
day.