From Longman Dictionary of Contemporary Englishpen somebody/something ↔ up/in phrasal verb1 TADto shut an animal in a small enclosed area2 be penned up/inLIMIT to be restricted or forced to remain in a small place Norma felt restless and penned in. → pen→ See Verb table
Examples from the Corpus
pen up/in• Craig and Johnson met the way practically anyone meets an inmate: They became pen pals.• Some of the small ones were ink-stained, and I realized that these had been for ink bottles and pens.• This grid enables the software to determine the position of the pen.• There was a dearth of pens that day in class.• The pen comes in it's own attractive slip case.• I m going to get a marker pen and colour in one side - hey presto, a KeaneKickmaster.• The tiny pens, scrawling in palsied traces on endless white ribbons of paper, slowly ground to a halt.• Where Peach's pen had been in the window was a cage with a snake in it, curled up on straw. 