ὑποπόδιόν [2 verses](noun sg neut nom) "Footstool" is from hypopodion, which means "footstool" and "to reduce under one''s feet." It was the practice of conquerors to place their feet on their conquered enemies' necks. -- -- The Greek word translated as "footstool" has one meaning as something that goes "under feet," which is its literal meaning. It is the subject of the phrase.  Jesusly uses this word twice. It has no article before it, nor a "his" modifying it, so the sense is that the planet is "a footstool" not "the footstool."

Ὑπόστρεφε [4 verses](verb 2nd sg pres imperat act) "Return" is hypostrepho, which means "turn round or back," "roll up," "return," "turn away," and "elude."  - "Return" is a verb which means "turn round or back," "roll up," "return," "turn away," and "elude." 

ὑποτάσσεται [1 verse](verb 3rd sg pres ind mp) "Are subject to you" is hypotasso, which means to "place","assign", "arrange under", "put in shelter of", "subject", "put after", "subjoin", and "append". -- A word only used once by Jesus is translated as  "are subject to you". It means to "place","assign", "arrange under", "put in shelter of", "subject", "put after", "subjoin", and "append".  It is in a form where its subject is singular, so "he places" or "he assigns." 

ὑψηλὸν [1 verse](adj (sg neut nom/acc) "Highly esteemed" is hypsēlos,  which means "high, "lofty", "stately", "proud", "upraised" and "mighty". -- The Greek adjective translated as "highly esteemed" means "high, "lofty", "stately", "proud", "up raised" and "mighty".  It is only used by Jesus here in the Gospels. Everywhere else it is used to refer to the height of a mountain. 

Ὑψίστου, [1 verse](adj sg masc gen irreg_superl) "Of the Highest" is from hypsistos, which  means "highest", and "loftiest". "Of the Highest" is a superlative adjective that means "highest", and "loftiest".