erratic
ih-RAT-ikadjMeaning not regular or predictable
Memory hook e-RAT-ic: a RAT that zigzags. The pet rat zigzags across the floor, left, right, back, around the sofa, so no one can guess where it will go next. Its path is erratic.
The old car’s erratic engine coughed, roared and then went silent.
In context Lin’s sleep became erratic during exam week: some nights she slept three hours, some nights eleven, and she never went to bed at the same time twice.
Similar unpredictable, irregular, inconsistent, uneven
Opposite steady, regular, consistent
From Latin erraticus, “wandering,” from errare, “to wander, to stray,” the root of error.