adj. 25B6; adjective
unreliable volunteers : UNDEPENDABLE, untrustworthy, irresponsible, fickle, capricious, erratic, unpredictable, inconstant, faithless.
an unreliable indicator : QUESTIONABLE, open to doubt, doubtful, dubious, suspect, unsound, tenuous, fallible; risky, chancy, inaccurate; informal iffy, dicey.