Words that have TH in the middle:

​

Gather
Mother
Father
Grandmother
Grandfather
Brother
Either
Neither
​Leather
Feather

Athlete
​Together
Lather
Tether
Breather
Northern
Southern
Rhythm
Smoothie
​Although

Weather
​Slither
Other
Bother
Clothing
Heather
Motherhood
Fatherhood
Soothing
Teething

Tithing
Loathing
Worth
Weatherman
Seething
Breathing
Rather
Smoothest
Bathing Suit
​Fathom