1) Plaintive – is an adjective used for describing melancholy, sorrowful tone

 The singer sang Plaintive melody 

 2) Plaque – flat metal on a wall as a memorial

 The monument bears a plaque with the name of all those who died.

 3) Plea – when you are begging for something in urgency (request)

 A plea for help.

 4) Plead – try to convince them to see it to your way

 She pleaded with him not to leave her.

 5) Plethora – abundance of something

 Some people have plethora of time but do nothing in their life.

 6) Plod – walk slowly , heavily deliberately

 You might plod through the snow to reach bus stop on time.

 7) Plumb – measure the depth or understand deeply

 Plumbing the mysteries of human psyche.

 8) Plummet – drop sharply

 Roller coaster that plummets down a hill.

 9) Plunge – to push something suddenly with force

 He plunged the knife into the table.

 10) Poignant – that touch you deeply 

 A poignant memory.