另外 / 另
Similarities
Both 另外 and 另 mean “another” or “other”, and both can be a pronoun or an adverb.
他一边说谢谢，一边从手里拿出另外一本书
他一边说谢谢，一边从手里拿出另一本书
Both sentences mean the same thing.
1. As pronouns
另外 + Number + Noun · 另外的 + Noun
另 + Number + Noun
另一本书 is correct; 另的书 is not — 另 does not take 的.
2. As adverbs
另找别人
另买一个
另外提供不少新的材料
另 usually goes with monosyllabic verbs; 另外 works with almost any verb.
3. As a conjunction
冬季应该注意多吃水果
另外，还要记得多喝水
另 cannot be used this way.
Quick comparison
| 另外 | 另 |
|---|---|
| pronoun, adverb and conjunction | pronoun and adverb |
| 另外的… is possible | 另的… is not |
| with many kinds of verb | usually with monosyllabic verbs |
另外 is the common, versatile form.
另 is the shorter one: 另一本, 另找, 另买.