Naming of perchloric acid
This nomenclature comes from a long time ago. In the $19$th century, it was decided that the acidic compounds containing H, O and another atom X would be named from the name of this third atom X.
If only one molecule of such an acid was known, the name would be made by adding the ending -ic. Example: Only one acid is known with a Carbon atom, and it is $\ce{H2CO3}$, which is called carbonic acid.
If two acids were known differing in the number of oxygen atoms, the most oxidized would follow the preceding rule. In the least oxidized, the ending would be changed into -ous. Example : In the $19$th century, the two following acids were known containing a nitrogen atom. Well  !$~\ce{HNO3}$ was called nitric acid and $\ce{HNO2}$ nitrous acid.
If more than two acids were known differing in the number of oxygen atoms, the chemists would copy the case of the chlorine atom, where four acids were known : $\ce{HClO, HClO2, HClO3, HClO4}$. In this case, the two acids situated in the middle of the list are named according to the previous method : $\ce{HClO2}$ is chlorous acid, and $\ce{HClO3}$ is chloric acid. For the two extreme cases, it was decided to add prefixes, hypo- for the lowest number, and per- for the highest number. As a consequence, $\ce{HClO}$ became hypochlorous acid, and $\ce{HClO4}$ was called perchloric acid.
Today, the same regulations is applied, but the criterion of the number of oxygen atoms has been replaced by the oxidation number. The suffix -ous and -ic must be used if the corresponding acids have a difference of $+2$ in their oxidation numbers.
It should also be mentioned that the previous nomenclature is valid for acids having only one X atom. If an acid have two X atoms, the prefix di- should be added, and tri- for three X atoms. For example, $\ce{H2S2O5}$ is called disulfurous acid, and $\ce{H2Cr2O7}$ is dichromic acid. There are also other prefixes like ortho- and meta- to distinguish between acids having one X and the same oxidation number, but a difference in the number of H atoms.