permanent marker; oil-based pen
A pen that uses oil-based ink, often synonymous with permanent markers. Compare 油性マーカー and 油性マジック, which are similar but may emphasize marker form.
I wrote my name on the box with a permanent marker.
This oil-based pen doesn't smudge even when wet.
oil paint; oil-based paint
Compound of 油性 (oil-based) and ペン (pen), a straightforward modern term.