Extended Strong's Greek Lexicon (Abbott-Smith based)
futile
Usage: μάταιος, -ον (as in Att.., but -αία, -αιον, 1Co.15:17, 1Pe.1:18; μάτην), [in LXX for שָׁוְא, הֶבֶל, כָּזָב, etc. ;] vain, useless: ἀνωφελὴς κ. μ., Tit.3:9; πίστις, 1Co.15:17; θρησκεία, Jas.1:26; διαλογισμοί, 1Co.3:20 (LXX); ἀναστροφή, 1Pe.1:18; of idols and heathen gods, τὰ μ. (Jer.2:5, 4Ki.17:15, al.): Act.14:15 SYN.: κενός, q.v (AS)