The plastic things on the end of shoelaces are called aglets

The word "aglet" (or "aiglet") comes from Old French "aguillette" (or "aiguillette"), which is the diminutive of "aguille" (or "aiguilee"), meaning "needle". This in turn comes from "acus", the original Latin word for needle. An aglet is thus like a small "needle" at the end of a cord. http://en.wikipedia.org/wiki/Aglet