You will find 7 meanings shown in OED's entry for that term greatest, amongst which happens to be labelled obsolete. See ‘That means & use’ for definitions, usage, and quotation proof. It was the longest one—in runtime—to reach the major British charts at that time, As well as in 2013, https://travisdlrxm.blazingblog.com/36104191/getting-my-the-greatest-song-ever-written-to-work