biker UK /ˈbaɪ̯kə/US /ˈbaɪ̯kɚ/ noun2 •A person whose lifestyle is centered on motorcycles, sometimes a member of a motorcycle club.There’s a wonderful sketch of a formidable biker called “Roundhouse,” who is “humongously fat and hasn’t had a haircut since third grade.” — 2004 •A cyclist. formsbikers