The Spanish word 'nena' meaning 'little girl' or 'baby girl' appears to be a term of endearment that likely originated from baby talk or nursery language. Like many words used to refer to babies or young children, it may have developed from the natural sounds that infants make.

A related Spanish word is 'niña', which also means 'girl' or 'little girl'. Both 'nena' and 'niña' are commonly used as terms of endearment in Spanish-speaking cultures.

While there aren't direct English cognates for 'nena', the English word 'nanny' (meaning a childcare provider) shares a similar pattern of using the 'n' sound in words relating to children and caregiving, though they aren't etymologically related.