Solder and soldier are easily confused words.
The spell-check application of most word processing software programs would not catch a slip-up of these two words. Spell-check is looking for words that aren’t in its dictionary, and words that resemble words in its dictionary but are possibly spelled wrong. Spell-check isn’t perfect. It doesn’t know and can’t guess what word you wanted or what word you meant, it can only judge the words on the page. If you used words that are all spelled correctly, it gives you a pass anyway.
Autocorrect suggests words that start with the same letters. It’s suggesting what word you may want to save time, but quite often, its suggestions are pretty off base. They don’t help you out, but they do make you laugh.
Solder (pronounced “sawd-err”) is a noun. It means a metal with a low melting point that is sold on spools. Solder is melted with en extremely hot iron for connecting electrical and other wires.
Soldier (pronounced “s-old-yer”) is a noun. It means a person in the armed forces, typically more land-based operations.
The following story uses both words correctly:
Sol wasn’t sure what he wanted to do after high school for a career, so he became a soldier in the Air Force. Flight had always fascinated him. Ultimately he wouldn’t be piloting the aircraft, but he built and repaired planes and weaponry. He found soldering working with his hands was really fulfilling. After he retired, he got into remaking and repairing vintage automobiles.