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