Originally “Banzai” means ten thousand years and has been used to cerebrate Emperors.
Westerns may know it as a “banzai” call for suicidal actions. Soldiers said “banzai” because they wanted to contribute their lives for Emperor Hirohito.
However, Banzai is used in our day to day life and most of the time it is nothing to do with an emperor. For example a candidate calls Banzai when he/ she is got a seat in Japanese house (diet). A popular song says “Banzai, I feel good because I met you. I am and will be happy until the last day of my life” - Banzai Kinimi Deaete Yokatta (by Urufuruzu). It just used to celebrate one’s fortune.
By the way, a bonsai is nothing to do with Banzai. Bon is a table and Sai is a something planted and therefore it just means a table trees.
One interpretation is that you’re asking about ‘banzai’; it’s written 万歳 in Japanese , which comes from an ancient chant for Chinese emperors, 萬歲 (the first character has been simplified in Simplified Chinese and Japan). It means ‘ten thousand years of age’ or, more accurately, ‘may you live forever’.
The Western usage of the term is used to refer to suicidal bayonet charges that were made by some Japanese units facing certain defeat; as they charged into death, they chanted this term in a somewhat similar manner to ‘allahu akbar’ of some terrorist groups when carrying out suicide bombings.
The other possibility is that you’re talking about ‘bonsai’, which is the Japanese version of 盆栽, a practice originating in China in which trees are planted in small pots and cultivated to stay small by fastidiously trimming/confining the roots. The term literally means ‘planting in a pot’.
