I thought that it was the hardest bacon I’d ever had, but it was a dream and it seemed that I was biting my smartphone. No wonder it was so hard.
This is a single kanji with an い on the end, meaning you know it's probably an adjective. What's the adjective form of stiff? It's stiff.
The reading is the same as a very similar word, 固い. So, if you can use that word to help you to remember, you'll remember the reading of this word in no time as well!