1
general::
Phrase(s): on tiptoe
standing or walking on the front part of the feet (the balls of the feet) with no weight put on the heels. (This is done to gain height or to walk quietly.) • I had to stand on tiptoe in order to see over the fence. • I came in late and walked on tiptoe so I wouldn’t wake anybody up.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
1. Eagerly anticipating something, as in The children were on tiptoe before the birthday party. [Late 1500s] 2. Moving stealthily, warily, as in They went down the hall on tiptoe. [Mid-1700s] Both usages transfer standing on one's toes to a particular reason for doing so; def. 2 alludes to moving more quietly in this fashion.
American Heritage Idioms