identity — ODE

identity /ʌɪˈdɛntɪti

▸ noun

(plural identities)

1 the fact of being who or what a person or thing is:

he knows the identity of the bombers

[mass noun] she believes she is the victim of mistaken identity.

▪ the characteristics determining who or what a person or thing is:

he wanted to develop a more distinctive Scottish Tory identity.

▪ [as modifier] (of an object) serving to establish who the holder, owner, or wearer is by bearing their name and often other details such as a signature or photograph:

an identity card.

2 a close similarity or affinity:

an identity between the company's own interests and those of the local community.

3 Mathematics (also identity operation) a transformation that leaves an object unchanged.

▪ (also identity element) an element of a set which, if combined with another element by a specified binary operation, leaves that element unchanged.

4 Mathematics the equality of two expressions for all values of the quantities expressed by letters, or an equation expressing this, e.g. (x + 1)2 = x2 + 2x + 1.

– ORIGIN mid 16th century (in the sense ‘quality of being identical’): via French from late Latin identitas, from Latin idem ‘same’.