Strong's G1500 — εἰκῆ (adverb)
eike (ei-kay`) adv.
1. idly, i.e. without reason (or effect)
[probably from G1502 (through the idea of failure)]
KJV: without a cause, (in) vain(-ly) 
Root(s): G1502 
Hebrew root: εἴκω
Occurrences: 6