Definition of "fiver"

fiver

/ˈfaɪvɚ/

noun
plural fivers
1. (slang) A banknote with a value of five units of currency.
  Quotations
  […] a gesture that had a sort of self-parodying wit about it: it was like trying to borrow a fiver, getting turned down, and asking to borrow fifty quid instead.
  1995, Nick Hornby, High Fidelity, London: Victor Gollancz, page 15
2. (slang, by extension) The value in money that this represents.
3. (colloquial) A clenched fist.
4. A mathematical puzzle played on a 5 × 5 grid.
5. (Islam) A Zaydi Shiite Muslim, who disagrees with the majority of Shiites on the identity of the Fifth Imam.
6. (religion) A person who gives five percent of their income or five hours a week of their time to charity (a reduction of ten percent tithing).