treacherous
Cross references: 1. faithless treach.er.ous \'trech-(*-)r*s\ aj 1: characterized by or manifesting treachery : PERFIDIOUS 2a: likely to betray trust : UNRELIABLE {a ~ memory} 2b: providing insecure footing or support {~ quicksand} 2c: marked by hidden dangers, hazards, or perils - treach.er.ous.ly av