Masteika

Perhaps irregularly from *Mąsteika. Then for the sake of thinking - see Mastvilà. Although a different origin is also possible, cf. lit. mastýti „pinti; raizgyti, narstyti; skeryčioti, mosikuoti; blaškytis“ (LKŽ VII 898) - see Z. Zinkevičius, 1977, p. 170.