Abbott-Smith Manual Greek Lexicon
μάτην (G3155)
2 μάτην (prop. acc. of μάτη , a fault , folly ), adv., [in LXX for הֶבֶל , שָׁוְא , etc.;] in vain , to no purpose : Mt 15:9 , Mk 7:7 (LXX) .†
G. Abbott-Smith, A Manual Greek Lexicon of the New Testament (1922) — public domain