Ceiling, sealing and roof

Ceiling is the inside top of a room.
This room has a low ceiling.

Sealing is the act of setting a seal.
Please, seal this box.

The roof is the upper covering of a building.
The roof of the house was blown off in the storm.

Clear and Clean
Clear means transparent or audible.
He spoke in a clear voice.
This lake has clear water.

Clean means free from dirt.
Give me a glass of clean water.
We should wear clean clothes.

Contagious and infectious
Contagious means something that is spread by contact or touch.
Chickenpox is highly contagious.

An infectious disease may spread in any way, and not just by touch. Note that these days both words are used with little or no difference.

Desert and dessert
Desert is a large stretch of sand.
Arabia is a vast desert.

Dessert is a sweet dish served at the end of a meal.
The hostess served dessert after the meal.

Doubt and suspect
To doubt is to think that something is unlikely.
I doubt whether I will be able to finish this job on my own.

To suspect is to believe that somebody is guilty.
I suspect that my servant has stolen my watch.

Exhausting and exhaustive
Exhausting means tiring.
Public speaking is very exhausting.

Exhaustive means comprehensive or complete.
This blog aims to provide an exhaustive account of the whole of English Grammar.

Facility and Felicity
Facility means effortlessness.
He speaks English with facility.

Facility can also mean something that serves a particular purpose.
A lot of facilities are available at the club house.
Felicity means intense happiness.
Only the virtuous can enjoy true felicity.

Fetch and bring
To fetch is to go and get somebody or something.
She went upstairs to fetch her cell phone.
Jack and Jill went up the hill to fetch a pail of water.

To bring is to carry somebody or something.
He brought his little daughter to the office.
Please bring me a glass of water.

Get, obtain, acquire and attain
Get is the general term indicating that somebody is given something.
Every parent wants his or her children to get a good education.

To obtain is to get something by making an effort.
He obtained his management degree from the US.

To acquire is to get possession of something. To attain is to achieve a goal or desired state usually with an effort.
Lord Buddha attained enlightenment at Gaya.