diehard
n. countable C1 Advanced US //ˈdaɪˌhɑɹd// UK //dˈaɪhɑːd// diehard
n. someone who refuses to change their mind or stop supporting something, even when it is no longer popular. You use this for people who stick to old habits or beliefs.
n. a person who remains loyal to a person, cause, or belief despite opposition or changing circumstances. Often carries a slightly negative connotation of being overly stubborn or resistant to progress.
He is a diehard fan of the local football team.
Despite the new technology, the office still had a few diehards who refused to use the cloud-based software.
The political party struggled to modernize its image because the diehards in the legislature were determined to preserve the traditional policies that had defined the organization for decades.
Deverbal from die hard.