noun
working together with one mind; united in purpose
A yojijukugo (four-character idiom) describing a group of people acting in complete unity, often with a shared goal or conspiracy. Slightly formal or literary.
彼らは一味同心となって改革を進めた。
They worked together with one mind to advance the reforms.
一味同心で事に当たれば、どんな困難も乗り越えられる。
If we tackle things united in purpose, we can overcome any difficulty.