1. 单位元：identity 等(式) | identity element 单位元 | identity law 同一律

2. 单位元素：identifying signature 识别特征信息 | identity element 单位元素 | identity matrix 单位矩阵

3. 恒等元素(*群论)：identity operation 恒等运算(*群论) | identity element 恒等元素(*群论) | identification 监定;证认

4. 恒等元素：Idempotent element同势元素 | Identity Element 恒等元素 | identity mapping 恒等映照

noun

1. an operator that leaves unchanged the element on which it operates

e.g. the identity under numerical multiplication is 1

Synonym: identityidentity operator