(verb) spout forcefully; travel by jet
The sense of speed associated with this word does not arrive in English until the mid-17th century. For Shakespeare, the verb had only one meaning:
"strut, swagger" - the original meaning that arrived from Latin, perhaps via French, in the 15th century.
This is the sense required when Belarius tells his sons that "The gates of monarchs Are arched so high that giants may jet through" (Cymbeline, III.iii.5). He does not mean they are moving through the gates at speed.
Similarly, Malvolio is not moving fast when Fabian says to Sir Toby, "How he jets under his advanced plumes!" (Twelfth Night, II.v.31). And when Cleon describes the people of Tarsus as "jetted and adorned" (Pericles, I.iv.26), he means "ornamented".
Shakespeare has one other use of this verb, as a phrasal verb, jet upon.
This is when Aaron says to the lords, "think you not how dangerous It is to jet upon a prince's right?" (Titus Andronicus, II.,i.64). Here it means "encroach upon" - a development of another early sense of the verb, to "project" or "jut out".