1: legal possession of land as one's own
2: manorial land actually possessed by the lord and not held by tenants
4: REALM sense 2, DOMAIN
How does one acquire a large vocabulary? The first rule is to read, read widely, and read worthwhile materials, especially old books and essays. The second rule is to look up every word the meaning of which you do not know or are not certain of: don't be lazy. The third rule is to compile vocabulary lists. The fourth rule is to review the lists periodically and put the words to use. Use 'em or lose 'em.
If you think you know the meaning of a word, you are well-advised to check your understanding. Even if you really do know the meaning of a word, you probably don't know all of its shades and variants.
If you work steadily at this, then perhaps someday you will have a vocabulary half as extensive as that of your humble correspondent.