particle
/ˈpɑ:tɪkl; `pɑrtɪkl/ n
1 very small bit or piece (of sth) 微粒; 粒子
particles of dust/dust particles 尘埃
He choked on a particle of food. 他让一小粒食物噎住了.
2 smallest possible amount 极少量
There's not a particle of truth in her story. 她讲的没有一句实话.
3 (also ad,verbial `particle) (grammar) word (eg away, back, down) used esp after a verb to show position, direction of movement, etc 副词小词（如away、 back、 down, 尤用於动词後, 表示位置、 运动方向等）
In `break down' and `tell sb off', `down' and `off' are adverbial particles. 在break down和tell sb off两词组中, down和off都是副词小词.