UNIQUE WORDS game to increase our vocabulary - alphabetical order

Washer - a small flat ring made of metal, rubber, or plastic fixed under a nut or the head of a bolt to spread the pressure when tightened or between two joining surfaces as a spacer or seal

Yak: a large, stocky, shaggy-haired wild ox of the Tibetan highlands, having long, curved horns; endangered

Alpenglow - the rosy light of the setting or rising sun seen on high mountains.

Caliginous - misty, dim; obscure, dark.

"the caliginous sky"

Elementary - 

1. relating to the basic elements of a subject.

   "an elementary astronomy course"

2. straightforward and uncomplicated.

   "a series of elementary exercises"

Guesstimate: an estimate based on conjecture

Indefatigable: having or showing a capacity for persistent effort; not tiring or relenting