"foot soldier," also "young male servant" (attested as a surname from c.1100), possibly from a Scand. language (cf. Norw. -ladd,
in compounds for "young man"), but of obscure origin in any case. OED hazards a guess on M.E. ladde,
plural of the pp. of lead
(v.), thus "one who is led" (by a lord). Meaning "boy, youth, young man" is from c.1440. Scottish form laddie,
a term of endearment, attested from 1546.