What is "Mushin"? 無心とは？

Have you ever heard of the term "mushin"? It's a Zen word, written as "無心" in Japanese Chinese characters (kanji). So, you may have heard of it if you're interested in Zen and/or Buddhism. Mushin can literally translate into "no mind" because 無 means non-existence and 心 mind. According to Kojien dictionary, mushin means as follows: 

1. The state of no mind, thought, or consideration 
2. Having no good taste
3. Not hesitating to ask for something, e.g., money
4. The state of no distracting thoughts 

As you can see, mushin is negative (i.e., 1 to 3) and also positive (i.e., 4) and in Zen (i.e., Buddhism), mushin means 4. Engakuji temple's website clarifies the meaning of mushin in the Buddhist context as follows: 

"In Buddhism, 'kokoro' (mind) means the function of kokoro. Therefore, mushin means not "no mind" but "no function of mind" or 'magokoro,' i.e., true heart, sincerity, and pure feeling, where distracting thoughts have been all destroyed.  

The kokoro (mind) sees the concrete and is fixated on it. The state of being rid of such fixation and out of feeling lost, that is mushin, enables the appreciation of the truth. (Translated by Kei Narujima and the rest omitted.)"  

Unfortunately, however, neither Kojien dictionary nor Engakuji temple's website tells how to achieve mushin but I believe it can be achieved (in a way) by being in a state of flow, i.e., a state of concentration or complete absorption with the activity at hand and the situation (the concept recognized by Mihaly Csikszentmihalyi [source; Wikipedia]). For example, when practicing aikido, I can be in a state of flow and after the practice, distracting (or any) thoughts that filled my mind with are all gone. After a yoga class, I also feel my mind ridded of any thoughts. Zazen or seated meditation must be of course a way to achieve mushin. 

Interestingly, mushin can also translate literally into mindlessness, the opposite of mindfulness, although mushin means almost the same as mindfulness and that is why it must be very difficult to understand what mushin represents without being said since their childhood "Be in the mushin state (meaning that destroy all distracting thoughts) and focus on what's in front of you." (It's like non-English speakers having difficulty mastering the use of articles.)    

For me, mushin, flow, and mindfulness (and neutral in a way, too) are mostly the same, which, however, poses another question about the relationship between mushin and Hannah Arendt's concept of "thinking." I have no answer for this question now. 

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