A tip, height, or extremity.
[Greek akron, a tip or summit.]
An acrobat (Greek bainein, to walk) is literally someone who walks on tiptoe; an acropolis (Greek polis, city) was a fortified part of an ancient Greek city, typically on a hill; an acronym (Greek onuma, name) is a word formed from the initial letters of a phrase.
In medicine, the acromion is the outward end of the spine of the shoulder blade. Medical conditions include acromegaly (Greek megas, great), abnormal growth of the extremities and face caused by excessive production of growth hormone, and acrophobia, extreme or irrational fear of heights.
Some words that look as though they include this prefix actually contain Latin acer, pungent or acrid: acrolein, a sharp-smelling liquid; acrimonious, of an angry or bitter exchange.