In Act II, scene iv of Shakespeare's As You Like It, Rosalind, in disguise as Ganymede, opens the scene by saying, "O Jupiter, how weary are my spirits!" Rosalind and Cecilia escaped together from Duke Frederick's court and have been traveling in disguise. In Act II they finally come upon Arden Forest (Rosalind: "Well, this is the forest of Arden"). Jupiter is the chief Roman god who is akin to the Greek god Zeus (though there are some differences between them) and was derived, as was Greek Zeus, from the earlier Egyptian god Ammon.
If taken literally, Rosalind calls "O Jupiter" as supplication to the god, then declares how weary (tired, worn out) from traveling she is. She says "spirits" because along with being physically tired, her heart is heavy from being betrayed by the Duke. Her supplicant posturing, a result of calling on Jupiter to attend to her, means that she is asking Jupiter to aid her weariness and her journey.
If taken figuratively, "O Jupiter!" is a meaningless exclamation equivalent to "O heavens!" or "Oh man!" that precedes exclamations of various kinds. In short, Rosalind is exclaiming emphatically about how tired she is from walking all that way and how sad she is.