[Casiopea]

1. any of a number of songbirds which imitate other bird’s calls.
=> a number of______(plural noun); 'which' is a relative pronoun. It stands for the noun 'songbirds'. We know this because we can replace 'which' with 'songbirds': which imitate other birds' calls => songbirds imitate other birds' calls. Please note, birds'. The apostrophe goes after the -s.

2. This bird imitates other birds' call. (calls belonging to other birds)
4. This bird imitates other birds call. (Odd. a plural noun is acting as an adjective)

5. Anisotrophic: having different physical properties at different levels of measurement. (Noun, general)

7. Dictionary meanings. (The book gives more than one meaning)
8. Dictionary meaning. (The meaning is from the dictionary)

9. (an) same idea
=> 'an' is non-specific. It means, 'any', whereas 'same' is specific, so use either one or the other, not both: 'an idea' or 'the same idea'. Note, 'the same' is a set pair.