1. the statement, the assertion (Something that people say)
2. the message (For texts, stories and movies)
3. the testimony (in law)
The original sense of the root was:
following, pursuing
If we think of this in a context of hunting, we can easily see why how this root evolved into the words to see (from following with eyes) and to say (telling what you see). The connection of “to say” is debated, though.
The original sense of following is well preserved in the Latin branch around *sequi (to follow) with words like sequence, sect or execute.
Also the words around social likely belong to this family.
Here’s an (incomplete) list of the relatives in English: