2. COMPARATIVE adjectives compare TWO things.
-er endings, more, less
SUPERLATIVE adjectives compare THREE or MORE things.
-est endings, most, least

3. Rules to follow when writing comparative or superlative adjectives:
For all 1-syllable and a few 2-syllable adjectives, add –er for comparative form or –est for superlative form.
If adjective ends with single vowel and consonant, double the consonant before adding the ending.
If adjective ends with consonant and y, change y to i before adding ending.
For most 2-syllable adjectives and all 3- or more-syllable adjectives, use more/less for comparative form and most/least for superlative form.
Never use both –er and more/less or –est and most/least with a single adjective.

6. (Meaning healthy)
, many