Keystone and Second base

Keystone noun - An immaterial thing upon which something else rests.

Second base and keystone are semantically related In some cases you can replace phrase "Second base" with "Keystone", this terms are similar.

Second base noun - The base that must be touched second by a base runner in baseball.

Keystone and second base are semantically related in second step in the baseball diamond topic. You can use "Keystone" instead a noun phrase "Second base".