Adjective that ends with a single consonant with a vowel before it
If the one-syllable adjective ends with a single consonant (medeklinker) with a vowel (klinker) before it, double the consonant and add –er for the comparative form; and double the consonant and add –est for the superlative form.
- Thin: Thinner / Thinnest
- Flat: Flatter/ Flattest