The Spanish word 'muchacha' (meaning 'girl') has an interesting etymology that traces back to the Latin word 'mutilus', meaning 'mutilated' or 'cut off'. This Latin word evolved into the Spanish word 'mocho', meaning 'cut off' or 'cropped'. From 'mocho' came the now obsolete Spanish word 'mochacho' meaning 'boy', which eventually led to the feminine form 'muchacha'.

The semantic evolution from a word meaning 'cut off' to one meaning 'girl' might seem strange, but it's believed that 'mocho' may have been used to refer to someone with cropped or cut hair, a characteristic that might have been associated with young people in medieval Spain. The vowel change from 'o' to 'u' in the first syllable ('mochacho' to 'muchacha') is a common phonetic development in Spanish.

A simpler related Spanish word is 'mocho', which is still used today to mean 'cut off' or 'cropped'. While 'mocho' is typically used for objects that have been cut or trimmed, its derivative 'muchacha' developed to specifically refer to a young girl. The masculine form 'muchacho' (boy) is also commonly used.

While there aren't any common English words directly related to 'muchacha' through the Latin 'mutilus', English borrowed the word 'mutilate' from the same Latin root. This helps show how words from the same origin can develop very different meanings - while 'mutilate' retained the negative meaning of cutting or damaging something, Spanish 'muchacha' evolved into a neutral term for a young girl.