Lepto is defined as thin.
An example of lepto is leptocephali, which is the ribbonlike larva of some marine animals.
thin, fine, slender: leptodactylous
also, before a vowel, lept-
Origin of lepto-Classical Greek lepto- ; from leptos, thin: see lepton
Slender; thin; fine: leptocephalus.
Origin of lepto-Greek, from leptos, fine, thin, from lepein, to peel.