Although I haven't listened to the podcast, I'd guess what he's trying to say here is the Latin word milites (meel-i-tays or meel-i-tez). This is the plural form of the Latin word miles, which was the standard translation of what would in the vernacular become 'knight'.

The reason this word is used untranslated, particularly in the eleventh century, is that the men who are called milites in the surviving documents are still quite a way away from what we would think of when we here the word 'knight'. They wouldn't have been dubbed or gone through any sort of ritual ceremony to achieve that status (although these sorts of ceremonies were starting to happen at the very top end of the social spectrum by the end of the eleventh century), they wouldn't have had any special code of chivalric conduct, beyond the general Christian morality preached to all lay people.

What milites were, however, is much trickier to answer and is still the matter of some considerable academic debate. The word itself is an old one and is derived from the Latin verb militare, 'to serve', and the most common translation before c. 900 is just 'soldier'. (It's also the root of the modern English word 'military'.) During the tenth century, and in some rare cases even before, it begins to be used as a title and indicator of some kind of special status; people sign their name as e.g. Rotbertus miles 'Robert the miles', instead of just plain old Robert. There's clearly some shift in meaning, but what exactly that was is difficult to say. Some would certainly call them proto-knights, vassals and dependents of the upper nobility and elite (in every sense) warriors; others argue that they were essentially nothing more than up-jumped bandits and brigands, using violence as a way to force themselves up the social ladder towards respectability. The consensus of the debate is probably closer to the former interpretation, but it remains ongoing.

For a good, readable introduction to this topic, check out chapter 3 of Richard Kaeuper's Medieval Chivalry.