In biochemistry, "amyl" means "pertaining to starch". Many moderately complex biological chemicals related to starch contain it, for example:-
Note that in this usage, it is a part of the word, and becomes "amylo" when preceding a consonant.
In organic chemistry, amyl is the old trivial name for the radical called pentyl under the IUPAC nomenclature: that is, -C5H11. This usage may derive from the presence of amyl alcohol in fusel oil, which is often fermented from starches. In this usage, amyl (normally) remains a separate word and it does not become "amylo-" before a consonant.
Several important amyl/pentyl compounds are still widely known by their older, amyl names, including:
"Amyl", used to mean "starch", was taken from Greek αμυλος = "cake made from fine flour", from α + μυλη = "not mill" because the flour used to make an αμυλος was not ground on the same grindstones as ordinary bread flour.