To rationalise

This verb is used of a psychological process whereby a person justifies with false reasoning an action which he or she wishes to take irrationally. In Jane Austen's Emma, the eponymous heroine wants to prevent Harriet Smith from marrying Robert Martin for selfish and meddling motives but rationalises her interference by telling herself that it is for Harriet's own good.

Trouthe

When reading Chaucer it is vital to realise that some words, which appear like modern English terms, have important differences in meaning. Trouthe does not mean truth but is a solemn promise on which a person's entire integrity resides and which must not be broken under any circumstances. The Franklin's Tale in The Canterbury Tales has its narrative base in two such conflicting promises.

MOOD and TONE

In literary analysis it is helpful to acknowledge or create a distinction between these terms:
mood represents the writer's feelings towards his/her subject matter; tone results from her/his attitude to the topic.
The mood might be sad or joyful or any other emotional state whilst the tone could be ironic, adulatory etc and is more a mental state.

DIMINUTIO

This is a rhetorical device used by speakers and by Chaucer in The Canterbury Tales whereby a character disparages his own skills, often claiming to be a blunt person, incapable of elevated discourse. This allows him to be crude or, alternatively, impressive with poetic language which comes as a surprise. The Franklin says he is a "burel" [plain, homely] man and yet tries to win admiration with a Tale about aristocrats with some rhetorical flourishes.  The device may still be heard when someone starts a speech: "Unaccustomed as I am to public speaking."

Consonant suffixes

Suffixes beginning with consonants do not often cause spelling problems: usually you tack them on to the end of a word without altering it: sincere + ly = sincerely
Exception: words ending in le change the le to ly: able/ably, subtle/subtly
Other exceptions: fully, truly, duly, wholly, argument
Common consonant suffixes are: ful, ness, ment, some, tion, sion, ly

Compliment and Complement

Both these can be used as nouns or verbs.
Compliment is the more common. It means to praise someone: He complimented her on her writing.
Complement means to add on and improve: The belt complemented her outfit. To remember the spelling, think of the word complete.

Prefixes

Prefixes are syllables which add on to the start of a word to change its meaning.
Usually you tack them on without any alteration: dis + appear = disappear 
Keep any double letters that result: dis + satisfaction = dissatisfaction

Common prefixes are: dis, un, mis, re, al (not all), pre, bi, semi, tri, ex, inter, post, trans

Some prefixes change their first letter to make the words easier to pronounce:
in + legal + illegal   in + mature = immature   sub + fix = suffix