The most common and most likely answer to this crossword clue is the 4 letter word PENS
P
E
N
S
More clues leading to the result PENS
Buddy explains!

The straight part
We know that "Imprisons" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case imprisons = pens.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PENS mean?
PENS noun- An enclosure (enclosed area) used to contain domesticated animals, especially sheep or cattle.
- A prison cell.
- The bullpen.
- To enclose in a pen.
- A tool, originally made from a feather but now usually a small tubular instrument, containing ink used to write or make marks.
- A writer, or his style.
- Marks of ink left by a pen.
- A light pen.
- The internal cartilage skeleton of a squid, shaped like a pen.
- A feather, especially one of the flight feathers of a bird, angel etc.
- A wing.
- To write (an article, a book, etc.).
- A female swan.
- Penalty.
- In the United Kingdom and Ireland, a copper coin worth 1/240 of a pound sterling or Irish pound before decimalisation. Abbreviation: d.
- In the United Kingdom, a copper coin worth 1/100 of a pound sterling. Abbreviation: p.
- In Ireland, a coin worth 1/100 of an Irish pound before the introduction of the euro. Abbreviation: p.
- In the US and Canada, a one-cent coin, worth 1/100 of a dollar. Abbreviation: ยข.
- In various countries, a small-denomination copper or brass coin.
- A unit of nail size, said to be either the cost per 100 nails, or the number of nails per penny. Abbreviation: d.
- Money in general.