Words For Granted - specifically an etymology podcast
And... Looked through my 300 or so subscriptions, couldn't find others by title. I recall @grammargirl Mignon Fogarty's podcast was often good for that, but I can't recall the title. Others cover word usage piecemeal sometimes, so no help there.
Betting Ms Fogarty would have better suggestions for podcasts about changes in word usage, nu?