Insidious.
Tenuous; rarefied; of low density or thin consistency.
Barely noticeable, not obvious, indistinct.
Cleverly contrived.
Cunning, skillful.
Hard to grasp; not obvious or easily understood.
Extremely reckless.
Likely to commit, or to attempt to commit, suicide.
Highly likely to certain to result in the deaths of the participants; dangerous or reckless to such a degree as to be tantamount to suicide for those taking part.
Pertaining to suicide.
Someone suicidal; someone likely to kill themselves.