Correct spelling, explanation: shield is not only a noun but also a verb. It must be spelled with two vowels: first -i, then -e. If you’re not careful enough, you can confuse their order. Sheild is a non-existent word, but some people may think this is the right spelling. If you want to be sure, just look at its etymology, especially Old English scield (shield).

Definition of shield:
1. noun, something that defends or protects someone or something
Our body’s immune system is a natural shield against any infection.
Medieval knights always wore shields.
2. verb, to protect from danger
My girlfriend’s parents always wanted to shield her from the dangers of this world.
I swear to shield you all my life.

Collocations with shield:
Some most commonly used collocations include: carrying a shield, behind the shield.
The police wore helmets and carried shields.
She was hiding behind her shield.

Incorrect spelling, explanation: there is nothing in the etymology to indicate that this spelling is correct. This word should contain two vowels in the following order: first -i, then -e, not vice versa. You need to be careful when writing it down, because the pronunciation may cause some confusion. Shield is the only correct version and sheild is incorrect.