571  apistos  ap'-is-tos

 from 1 (as a negative 
particle) and 4103; 
(actively) disbelieving, i.e. 
without Christian faith 
(specially, a heathen); 
(passively) untrustworthy 
(person), or incredible 
(thing):--that believeth not, 
faithless, incredible thing, 
infidel, unbeliever(-ing).

 see GREEK for 1

 see GREEK for 4103