Check the Oxford English Dictionary to: 1) read definitions of the 5 unusual words in contemporary English that you've selected for the assignment, 2) make sure the 3 "new" words you've selected are not in the dictionary:
Online dictionary covering meaning, history, and usage of words across the English-speaking world.
Use resources like these to find etymological information and write "biographies" of your chosen words/phrases:
An Analytic Dictionary of English Etymology: An Introduction by 
Find even more reference books on etymology with this subject: English language -- Etymology -- Dictionaries
The Insect that Stole Butter?: Oxford Dictionary of Word Origins by 
