He contemplated marrying his cousin ' Here marrying ' is-

Gerund:

Verb-এর সাথে ing যুক্ত হয়ে তা যদি একইসাথে verb এবং noun-এর কাজ করে তবে তাকে gerund বলে । 

For example-

Reading is an excellent habit.

Gerund/Noun একটি বাক্যে পাঁচটি অবস্থানে বসে:

1. Sentence এর subject হিসেবে gerund বসে। 

For example:

Walking is called the best exercise.

2.Sentence এর object হিসেবে gerund বসে। 

For example:

 It has stopped raining. 

3.Preposition এর object হিসেবে gerund বসে।

For example:

The customers grew tired of waiting.

Be is fond of riding bicycle.

There is no credit in earning money illegally.

4.Complement হিসেবে gerund বসে।

For example:

Seeing is believing.

His profession is teaching.

My favorite activity is riding bicycle.

5.Compound noun হিসেবে gerund বসে।

For example: 

Walking stick has been lost.

Taking exercise is a good habit.

Making tea can be your earning source.