a.

1. 偶然的；意外的
   Breaking the vase was purely accidental; she did not mean to do it.

   打碎花瓶纯粹是偶然失手；她无意弄坏它。

2. 非主要的；附属的；附带的
   accidental benefits

   附带优惠

3. 【音】临时符号的

n.

1. 非主要的特性，次要方面
2. 【音】临时符号[C]

adj.

1. happening by accident.
2. incidental.
3. Philosophy  relating to or denoting properties not essential to a thing's nature.

n.

1. Music  a sign indicating a momentary departure from the key signature by raising or lowering a note.
2. Ornithology  another term for vagrant.