Soldier and solider have very different meanings and pronunciations, but they are often confused because of their similar spelling.
A soldier is someone who fights in an army, e.g. He was a soldier in WWII.
Solider is the comparative form of the adjective 'solid' and is used to say that something is 'more solid'.
Common things that are described as 'solider' are foundations, performances, and evidence. e.g. They should have built the house on a solider foundation than silt.
The Difference Between Solider and Soldier
The soldiers fought bravely in the battle.
The adventurers soldiered on through the tough terrain to find the treasure.
Solider is a comparative adjective related to the word solid. It means more solid. Some dictionaries do not recognize this form of the word solid, while others do.
It is correct to use either solider or more solid when writing. However, solider often sounds strange to English speakers, so you may prefer to use more solid.
Solider and Soldier Synonyms
I hope the sequel has a solider plot than the first movie. OR I hope the sequel has a more solid plot than the first movie.
Wise people build their houses upon solider foundations. OR Wise people build their houses upon more solid foundations.