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

Deeply

Pronunciation: diːplɪ

Kind of word: adverb

Formal definition:
Far down or in.

Informal definition: 
When you are in love,  you are deeply about that person, animal or something.

Example: 

• the baby is sleeping deeply.

 Related words: 

• profoundly
• greatly
• enormously
• extremely
•  very much
• strongly
• powerfully

Song/Video:

https://www.youtube.com/watch?v=-xwc-WJE_WI


Another link example: 

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