Monotonous

Pronunciation: məˈnɒtənəs

Kind of word: Adjective
 

Formal definition: dull, tedious, and repetitious; lacking in variety and interest.

 
Informal definition: Something that is boring.

Example:

- His voice was monotonous , expressionless and cold.

Synonym:

• monotone
•  drab
• dreary
•  humdrum
• singsong

Song or video:

https://www.youtube.com/watch?v=PqEQWC_6yYQ

Another link:

https://www.youtube.com/watch?v=lrqwZqJEPWE

Mellow

Pronunciation:  meləʊ

kind of word: Adjective, adverb and verb

Formal definition: pleasantly smooth or soft; free from harshness, make or become mellow.
Informal definition: something very sweetness

Example: 
 
Even the period instruments used are distinguished by their mellow sound.

Synonym:

•  melt
• dulcet
• sweet-sounding
• tuneful
• melodious

Song or video:

https://www.youtube.com/watch?v=7CG2Z6Aeuvs
Another link:
https://www.youtube.com/watch?v=RzicY40FKkE

Misleading

Prounciation: mɪsˈliːdɪŋ

kind of word: Adjective and Verb

 Formal definition: inteded to deceive; fed the spy misleading information.

Informal definition: Some who tells lies.

Examples: The teacher had accidentally taught some misleading information to the students.

Synonym:

•  wrong 
• erroneous 
• incorrect 
• mistaken 
• misleading 
• false

Song/Video
https://youtu.be/gIhWk86R9Ao

Mature

Pronunciation:/məˈtjʊəʳ/

Kind of word: Noun

Formal definition:
"fully developed in body or mind; complete in development."

Informal definition:
"When someone is completely responsible about itself"

Example:

• Mature enough to take care of herself when she came home from school

Related words

• Ready
• Seasoned
• Ripe
• Full-grown
• Grow up

Song/video:
https://www.youtube.com/watch?v=tndB1J3UfUw

Link to other dictionaries/sites
http://www.macmillandictionary.com/dictionary/british/mature_1