The Spanish word 'tanto' (meaning 'so much' or 'so many') comes directly from the Latin word 'tantus', which meant 'so much' or 'so great'. This is a straightforward inheritance where both the form and meaning have remained remarkably stable over time, with just a minor shift from Latin '-us' to Spanish '-o' ending, following regular sound changes between the languages.

Some common Spanish phrases using 'tanto' include 'tanto tiempo' (so much time), 'mientras tanto' (meanwhile), and 'en tanto que' (while, whereas). The word is also used in the comparative form 'tanto... como...' meaning 'as much... as...', making it a fundamental word for making comparisons in Spanish.

While English doesn't have any direct cognates of 'tanto', we do use some borrowed Latin phrases that contain its ancestor 'tantus', such as 'tantamount' (which literally meant 'amounting to as much' and now means 'equivalent to'). The word 'tandem' (as in 'working in tandem') is also related, originally referring to horses harnessed one behind the other, from a Latin phrase meaning 'at length'.