Common_Errors_in_English_usage

quite right, but it may be difficult to get people to say anything else.
"PIN" was invented to meet the objection that a "password" consisting of
nothing but numbers is not a word. Pronouncing each letter of the
acronym as "P­I­N" blunts its efficiency. Saying just "PIN" reminds us
of another common English word, though few people are likely to think
when they are told to "enter PIN" that they should shove a steel pin
into the terminal they are operating. In writing, anyway, PIN is
unambiguous and should be used without the redundant "number."
The same goes for "VIN number"; "VIN" stands for "Vehicle Identification
Number." And "UPC code" is redundant because "UPC" stands for "Universal
Product Code."
PINNED UP/PENT UP
If you wear your heart on your sleeve I suppose you might be said to
have "pinned up" emotions; but the phrase you want when you are
suppressing your feelings is "pent­up emotions." Similarly, it's pent­up
demand." "Pent" is a rare word; but don't replace it with "penned" in
such phrases either.
PIT IN MY STOMACH/IN THE PIT OF MY STOMACH
Just as you can love someone from the bottom of your heart, you can also
experience a sensation of dread in the pit (bottom) of your stomach. I
don't know whether people who mangle this common expression into "pit in
my stomach" envision an ulcer, an irritating peach pit they've swallowed
or are thinking of the pyloric sphincter; but they've got it wrong.
PITH AND VINEGAR/PISS AND VINEGAR
To say that people are "full of piss and vinegar" is to say that they
are brimming with energy. Although many speakers assume the phrase must
have a negative connotation, this expression is more often used as a
compliment, "vinegar" being an old slang term for enthusiastic energy.
Some try to make this expression more polite by substituting "pith" for
"piss," but this change robs it of the imagery of acrid, energetically
boiling fluids and conjures up instead a sodden, vinegar­soaked mass of
pith. Many people who use the "polite" version are unaware of the
original.
PLAIN/PLANE
Both of these words have to do with flatness. A flat prairie is a plain,
and you use a plane to smooth flat a piece of wood.
"Plain" is also an adjective which can describe things that are
ordinary, simple, or unattractive.
But whether you go the airport to catch a plane or meditate to achieve a
higher plane of consciousness, the meanings that have to do with things
high up are spelled "plane."