Siphon and cypher 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.
Siphon is a verb. It means to use a tube and air suction to drain liquid from a container. Suction can be enabled by a vacuum, or more often, one’s mouth to get the liquid to start flowing.
Cypher is a noun. It can mean a coded or encrypted language. It can mean numbers. in relation to people, it can mean a person of little significance.
The following story uses both words correctly:
Cillian wasn’t sure what his career in life would be, at times he felt like a cypher, or the black sheep of the family. He had a knack for siphoning gas from cars, which helped with his lawncare business.