The Spanish word 'mientras' (meaning 'while') comes from a fascinating combination of two Latin words: 'dum' (meaning 'while') and 'interim' (meaning 'meanwhile'). These two words combined in Latin as 'dum interim', which then underwent several transformations in Old Spanish.

The Latin phrase first evolved into Old Spanish 'domientre', which then changed to 'demientre' and later 'demientra'. This was further simplified to 'mientra', and finally the modern Spanish 'mientras' was formed by adding the adverbial suffix '-s'.

This evolution shows how a two-word Latin phrase was gradually compressed and simplified over time to become the single Spanish word we use today.

The word 'mientras' is quite fundamental in Spanish and doesn't have many simpler related words in modern Spanish. However, you might occasionally encounter the slightly shorter form 'mientra' in some regional varieties of Spanish, though 'mientras' is the standard form.

The English word 'interim' is directly related to one of the Latin ancestors of 'mientras'. While 'mientras' developed to mean 'while', the English word 'interim' kept its original Latin meaning of 'meanwhile' or 'in the meantime'. You can remember 'mientras' by thinking about how both words relate to temporary periods of time.