Word for disproportionate punishment?

I read about somebody who was sentenced and put in prison for a very long time for a petty crime. I think the word began with a p...

The word means punishing somebody in a completely disproportionate manner.

For example, Matthew stole a candy bar from a 7-Eleven and got put in jail for 17 years.

Solution 1:

Draconian

https://www.vocabulary.com/dictionary/Draconian

Draconian Use the word Draconian (or lowercase draconian) to describe laws or rules that are really harsh and repressive.

In ancient Athens, Draco was a guy who made some seriously strict laws. So rules that are too restrictive — or just plain unfair — are called Draconian. Sentencing someone to 10 years in prison for littering would be Draconian. Some people think Singapore's chewing gum ban is Draconian.

This is a strong word, so if your parents make you do chores, they aren't being Draconian. But if they make you do chores for five hours every day, that's another story.

Solution 2:

The word you are seeking is disproportionate.

OD:

disproportionate: too large or too small in comparison with something else: ‘people on lower incomes spend a disproportionate amount of their income on fuel’ ‘persistent offenders were given sentences that were disproportionate to the offences they had committed’

Your example, "Matthew stole a candy bar from a 7-Eleven and got put in jail for 17 years," exemplifies a disproportionate punishment ... and the concept of disproportionality.

Solution 3:

I think the word you are half-remembering is punitive - inflicting or intended to inflict punishment; retributive, punishing (OED).

Note, however, that punitive means 'punishing' and not 'disproportionately punishing'. Even when used in law (as in punitive damages) the sense is that punitive damages compensate the wronged party and also punish (within reasonable bounds of proportionality!) the wrong-doer.

To have the sense sought by the OP you would need to say something like excessively punitive.

Setting aside the OP's request for a word beginning with 'P', draconian seems like the best fit for the sense described.

Solution 4:

Another phrase you might have heard is cruel and unusual punishment. It's a little more than simply disproportionate but it's a related concept and an important term of art in (international) human rights law.

Solution 5:

Unfitting

"He was given 30 years for stealing an apple? That seems unfitting."