說定

to agree on / to settle on

to set / to fix / to determine / to decide / to order

to persuade

to speak / to say / to explain / to scold / to tell off / a theory (typically the last character in a compound, as in 日心說|日心说 heliocentric theory)

to speak; to talk; to say / to explain; to comment / to scold; to tell off / (bound form) theory; doctrine