-er for learners of EnglishPowered by COBUILD (-əʳ)
You add-er to many short adjectives to form comparatives. For example, the comparative of 'nice' is 'nicer'; the comparative of 'happy' is 'happier'. You also add it to some adverbs that do not end in -ly. For example, the comparative of 'soon' is 'sooner'.