Displaying insight or discrimination; acute; penetrating.
That can or does physically penetrate something; piercing, penetrating.
That can penetrate opposition defences.
Pertaining to sexual activity involving penetration by the penis.
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.