Abbott-Smith Manual Greek Lexicon
ἄπειρος (G552)
1 ἄπειρος , -ον ( ἀ- neg., πεῖρα , trial ), [in LXX: Nu 14:23 , Za 11:15 ( אֱוִילִי ), Je 2:6 ( עֲרָבָה )*;] without experience of : c. gen. rei, He 5:13 (MM, VGT , s.v.).†
G. Abbott-Smith, A Manual Greek Lexicon of the New Testament (1922) — public domain