The Spanish pronoun 'se' has a dual origin, serving both as a reflexive pronoun and as a third-person dative pronoun. As a reflexive pronoun (meaning 'oneself'), it comes directly from the Latin reflexive pronoun 'se', which itself was related to the Latin 'sui' meaning 'of oneself'. The dative pronoun usage (meaning 'to him/her/them') evolved through a different path: from the Latin demonstrative 'ille' ('that'), which had a dative form 'illi'. This evolved into Old Spanish 'ge' before finally becoming 'se' in modern Spanish.

This dual etymology explains why 'se' can be used both for reflexive actions (like 'lavarse' - to wash oneself) and as an indirect object pronoun (like in 'se lo di' - I gave it to him/her).

Several common Spanish pronominal verbs use 'se' as a reflexive pronoun, such as 'sentarse' (to sit down), 'llamarse' (to be called/named), and 'irse' (to leave). The 'se' in all these cases indicates that the action reflects back on the subject.

While English doesn't have a direct cognate of 'se', we can find related words through the concept of self-reference. The English words 'self' and 'same' are distantly related to the Latin 'se' through their Proto-Indo-European roots, all expressing the concept of identity and self-reference. This connection can help English speakers understand the reflexive nature of 'se' in Spanish.