Definition of as:
(n) :
libra; a
bronze coin of the Roman republic, originally weighing one libra; but reduced, after the first Punic war, to two ounces; in the second Punic war, to one ounce; and afterwards to half an ounce
"you're heavier than I am, and not as tall."
(conjunction) :
in the same way that; according to what; at the same instant that;
when
"as you wish, my lord!"
"you are not as tall as I am."