C’mon, Get Happy: 7 Happy Expressions Defined
Happy as a clam

Happy hour

Slaphappy

Trigger-happy

Happy-go-lucky

Happy medium

Happy camper

Source and images
168 Color terms in English
Compiled by Stephen Chrisomalis
This list contains 168 definitions of obscure colour terms using combinations of ‘normal‘ colours of the rainbow and descriptive adjectives; e.g. cardinal = deep scarlet red; russet = reddish brown. Note that most English speakers outside the U.S. spell colour with the added British ‘u’ rather than the American version color. Don’t worry if the colours (or colors) in your universe don’t match up with the definitions I’ve given for these words, though – I’ve been known to have skewed perceptions of reality … Read More…
Synonyms for the 96 most commonly used words in English

Amazing — incredible, unbelievable, improbable, fabulous, wonderful, fantastic, astonishing, astounding, extraordinary
Anger — enrage, infuriate, arouse, nettle, exasperate, inflame, madden
Angry — mad, furious, enraged, excited, wrathful, indignant, exasperated, aroused, inflamed
50 Most Challenging Words

Back in 2010 The New York Times published a list of 50 fancy words that most frequently stump their readership.
The New York Times 50 Fancy Words
(defined and used)
1. Inchoate: just begun and so not fully formed or developed
I am glad your inchoate proposals for integrating the company were not accepted this time, thus saving us face. Read More…
Positive Personality Adjectives List

List of 100 common personality adjectives that describe people positively
You may use them for inspiration or to enhance your resume.
In reply to Important Infrequently Used Words To Know Rochelle commented that she would like to to see a list of joyful words she should learn as well.
So, let us have them:
A
adaptable –adj able and usually willing to change
Synonyms: compliant, flexible, malleable, resilient, versatile
adventurous –adj daring, risk-taking
Synonyms: adventuresome, audacious, bold, courageous, enterprising, intrepid, risky, brave