Fien is a person who is addicted to something. Games, TV shows, phones, substances, Etc. Fien is a term used to describe someone who is obsessed with something. There can be a single word with multiple meanings (polysemy words). Fien is a word like that.
Fien is not really a word from the traditional dictionary. The word in dictionary is fiend, that gives a slightly different meaning to the meaning associated with Fien. The word Fien is originated from Normand / English slang.

Apart from being a polysemy word, Fien, is one of the most frequently misspelled words in the USA, Fein which stands for Federal EIN is frequently misspelled as fien.
Let’s look at other meanings/people/activities / misspelled words associated with the word fien.
What is a Fein? Federal EIN (Fein) Number
FEIN is an abbreviation for “federal employer identification number.” This number is issued by the federal government and is used to identify your company on tax and payroll forms. EINs are also issued by some states. These numbers perform the same function as federal EINs.
Your Fein is a one-of-a-kind number that the Internal Revenue Service uses to identify your company.
Once you’ve obtained a Fein, you can use it on your company’s or organization’s tax filings, as well as enroll in the electronic federal tax payment system, which allows you to make tax payments quickly over the phone or online.
Your Fein is also required for payroll paperwork, and you cannot hire staff unless you have a Fein. It’s worth noting that if you run a small partnership or an unincorporated sole business, you can pay subcontractors without a Fein.
If you wish to join Fein, you can do so by clicking here.
Federal EIN (FEIN) Number Application – Business Help Center (irs-taxid-numbers.com)

Sinn Féin
Sinn Féin is a republican and democratic socialist Irish political party that is active in both the Republic of Ireland and Northern Ireland.
Arthur Griffith created the original Sinn Féin group in 1905. During the Irish War of Independence, its members established the revolutionary Irish Republic and its parliament, the First Dáil.
Following the Irish Civil War, the party separated, giving rise to the two traditionally powerful parties in Irish politics: Fianna Fáil and Cumann na nGaedheal. The current Sinn Féin party emerged from another split in 1970, with the opposing section eventually becoming the Workers’ Party.
Casey Fien
Casey Michael Fien, born October 21, 1983, is a former professional baseball pitcher from the United States. He played for the Detroit Tigers, Los Angeles Dodgers, Philadelphia Phillies, Seattle Mariners, and Minnesota Twins in Major League Baseball.
Fien attended La Palma’s John F. Kennedy High School. He went to William Penn University, Golden West College, and Cal Poly San Luis Obispo for college.
Nathan Fien
Nathan Fien (born 1 August 1979) is a former New Zealand international rugby league footballer who played in the 2000s and 2010s as a five-eighth and halfbacks.
He most recently played in the National Rugby League for the St. George Illawarra Dragons. He was a former Queensland State of Origin halfback, or five-eighth, who previously played club football with the North Queensland Cowboys and the New Zealand Warriors before joining St. George in 2009. He was a member of New Zealand’s World Cup-winning team in 2008.
Fien van Eynde
Fien van Eynde (born September 8, 1998) is a Belgian professional cycling rider who currently competes for the UCI Women’s Continental Team Doltcini-Van Eyck-Proximus.
At the 2020 UCI Road World Championships, she competed in the women’s road race.
Fien Troch
Fien Troch was born in Flanders, Belgium, (May 11, 1978). She is a director and writer who received multiple nominations and awards after graduating from the Sint-Lukas art academy in Brussels in 2000.

How to Use the Word Fien in a Sentence – Examples
She’s a game fien.
When it comes to viewing movies, he is a fien.