"untrusting, suspicious, alert," 1718, originally slang, with -y (2), and perhaps from dialectal lere "learning, knowledge" (see lore), or from leer (v.) in some now-obscure sense. OED suggests connection with archaic leer (adj.) "empty, useless," a general Germanic word (cf. German leer, Dutch laar), of unknown origin.
Untrusting; suspicious; wary: He was leery of toting so much money/ Cheyfitz and Farrell exchanged leery glances
[1718+; probably fr British dialect lere, ''learning, knowledge'']