Velishestve alone is "highness" indeed, however Russian protocol will modify one's "level" of "Velishestve-ness". Thus "Imperalanye Velishestve" for the Emperor equal to the English "Majesty" or "Gosudar Velishestvye" etc.
Alas, I have to respectfully disagree with F.A. regarding « Majesty » and « Highness » , so here’s my Russian lesson for today (using the Old Style Russian alphabet & grammar and bold letters for stressed syllables in transliterations):
Speaking about the Emperor : Его Императорское Величество « E
vo Impe
ratorskoe Ve
lichetsvo » (not « Imperalnye ») = His Imperial Majesty. It sounded like : Ye-VO Impe-RA-torskoye Ve-LI-chestva.
Speaking TO the Emperor : Ваше Императорское Величество «
Vashe Imper
atorskoe Ve
lichestvo » = Your Imperial Majesty. It was often shortened to Evo/Vashe Velichestvo (His/Your Majesty) after having used the longer version once in a conversation.
Speaking about an Empress : Ея Императорское Величество « E
ya (sounded like « yeYO ») Impe
ratorskoe Ve
lichestva » = Her Imperial Majesty
Speaking to an Empress : as "Velichestvo" is neutral in Russian, same as to an Emperor i.e. « Vashe Imperatorskoe Velichestvo » (Your Imperial Majesty).
As in English, the Russian language makes a difference between Majesty (« Velichestvo ») & Highness (« Vysochestvo ») but goes even further. Grand Dukes and Grand Duchesses were « Imperial Highnesses » thus : Его / Ея Императорское Высочество « E
vo/E
ya Impe
ratorskoe Vy
sochestvo » & «
Vashe Impe
ratorskoe Vy
sochestvo » (His / Her Imperial Highness & Your Imperial Highness).
The only « modification of level of highness », as FA puts it, wasn’t between Majesty & Highness but rather between princes of the Imperial Family. In 1886, for financial reasons, Alexander III reformed the Statute of the Imperial Family and restricted the title of Grand Duke (or Grand Duchess) to the siblings of an emperor, his children along with his grandchildren in the male line only.
Children of 2nd generation Grand Dukes (i.e. great-grandchildren of an emperor), along with elder sons of males only from the 3rd generation (i.e. elder great-great grandsons) were henceforth to be know as Князь / Княжна Крови Императорской « Knyaz’ / Knyazh
na Krovi Impe
ratorskoï » Prince / Princess of the Blood Imperial (styled Prince or Princess of Russia). They kept the title of Highness («Vysochevsto») but WITHOUT the « Imperial » part : thus they were addressed as Ваше Высочество «
Vashe Vy
sochestvo » = Your Highness.
ALL other members of the Imperial Family in the male line were Princes or Princesses of the Blood Imperial too (Princes / Princesses or Russia) but with the new title of Свѣтлостъ «Svetlost’ » (instead of «Vysochestvo »). As it means « clearness, lucidity, serenity », it’s translated as « Serene Highness » which could seem, in English at least, to be higher in rank than a simple « Highness » but it wasn’t the case in Russian as « Vysochestvo » was known to be higher in the pecking order. « Svetlost’ » being feminine, these princes & princesses were all adressed to as Ваша Свѣтлостъ «
Vasha
Svetlost’ ».
I might add that princes not of imperial blood, as well as counts and dukes were Сiятелъство « Siyatel’stvo » (which mean « excellence » but their form of address Ваше Сiятелъство «
Vashe Si
yatel’stvo » was formally translated as « Your Illustrious Highness » instead of Your Excellency.