Select the most appropriate meaning of the given idiom.

Speak one’s mind

to voice one’s thoughts plainly

The most appropriate meaning of the idiom "speak one's mind" is to voice one's thoughts plainly. It is an informal expression that means to say what you think, even if it is not what other people want to hear. The idiom is thought to have originated in the 18th century, and it is believed to be a reference to the fact that people often speak from their hearts, without censoring their thoughts.

The other options for the meaning of the idiom are incorrect. Speaking without thinking does not involve voicing one's thoughts plainly. Speaking in an as is not the same as voicing one's thoughts plainly. Putting one's thoughts in writing does not involve voicing one's thoughts plainly.