One thing that always makes story worlds feel more real for me is their special language. So when I created the world of the Darkly Fae, I started keeping a fae glossary of the non-English (or non-human) words and phrases I used in the series.
Since the magical Darkly Fae are inspired by Celtic mythology, I knew they would need some unique words and phrases stemming from that culture. Especially since they are quite insulated from the modern world.
This fae glossary includes some of the Gaelic-ish (because, really, I don’t speak Gaelic and I could be getting it all wrong…) terms you’ll find in the Darkly Fae series.
Fae Glossary
Aetherworld — the fae light realm
ainmhi — a fae’s animal form
aislingeach — dreamer, one who can see the fae realm in their dreams
comhaontu — the accord signed to eradicate the dark clan and makes the unjustified killing of any fae a magic-stripping offense
Everdark — the fae dark realm
folaigh — shielding magic
la ainmhi — the one day each month that a fae must spend in animal form to maintain their magic
maru iobartach — killing a human for magical gain
seelie — light fae, fae that receive a magical charge from positive human emotions such as joy and love
seomra rioga — the royal hall
siceach — future-sight, the ability to see and predict the future
Tastail Tine — Trial of Fire
Trocaire — the vow to not kill a human for magical gain
uile-iditheach tine — all-consuming fire, a method of execution
unseelie — dark fae, fae that receive a magical charge from negative human emotions such as pain and sadness
As you can see, I love making up words. Especially ones that use real words as the base.
In my Oh. My. Gods. and Sweet Venom series, a lot of the terms (like the names of the Dynamotheos Powers) are based on Greek or sometimes Latin roots.
In the underwater mermaid world of Thalassinia, they not only use a lot of ocean-themed slang words (check out the Sea Slang Glossary) but also most of the character names are based on common and/or scientific names for marine life.
If you want to see these words and phrases in action, read the Darkly Fae series. Start by grabbing When Magic Sleeps, the first book, for free.
If you want to print out the Fae Glossary, grab the PDF version.