DISCREET and DISCRETE

Discreet is used of a person who can keep a secret or is reliably cautious in conversation: He is very discreet and I can confide in him safely.
Discrete means separate or distinct: She has many friends but never sees them all together; she keeps them in discrete groups.

LITOTES

This term is pronounced with three syllables and long vowels and means understatement. It is often used with a negative: he is not a generous man - meaning he is very mean.
This idiom is common in Chaucer who says of the Clerk of Oxford ; "he nas nat [was not] right fat ", indicating that the man was extremely thin.
(Note that double or even triple negatives do not cancel each other out in late Middle English; they merely emphasize.)

AMBIVALENT and AMBIGUOUS

Ambiguous is used of a speaker or writer who does not make his or her meaning clear, possibly deliberately to give two meanings.: His sentence was ambiguous and nobody knew which way to take it.
Ambivalent is used of a person having contradictory feelings: I was ambivalent about the matter, partly supporting him and partly rejecting his message.

SOLILOQUY

This is a speech uttered when a character is alone on the stage or is addressing the audience rather than the other players. Its function is usually to reveal inner thoughts and the apron-fronted stage of an Elizabethan theatre lent itself to this purpose.
For my analysis of the famous soliloquies in Hamlet visit: http://www.classicsenglishliterature.com

ALTAR AND ALTER

These two words are pronounced the same but have very different meanings:
Altar is the holy table in a church: you can remember it by thinking that marriage has ar in it also.
Alter means to change something.

THE DOUBLING RULE NUMBER TWO

This rule deals with words of more than one syllable ending in one vowel and one consonant:
a) if the word ends in l double it; label labelling
b) if the stress in the word falls on the final syllable of the base word double the consonant:
begin beginning
c) do not double if the stress falls earlier; garden gardening
N.B. prefer preferring preferred preference
Tip: put the back of your hand underneath your chin to sense the stress

This is a difficult rule to master but worth the effort as it covers a large number of useful words and has few exceptions.

THE DOUBLING RULE NUMBER ONE

This is sometimes called the 1-1-1 rule because you are dealing with words of:

one syllable - one vowel - ending in one consonant;  hop
Double the final consonant hopping
but do not double x y w

(The reason for the rule is that the vowel in the ending cannot get back past a double consonant to make the vowel long (as it does in hoping meaning wishing for or in jumping where there is already a double consonant).
Remember: I was hoping for a sunny day and hopping up and down with with impatience.