For a small, emphatic word it is surprising that this is one which appears to have little if any use. That's possibly because it is largely Scots and northern dialect. So what does it mean?
- The backside or buttocks.
- The tail or scut of a hare, rabbit, etc.
- Woollen waste for mixing with mungo and shoddy. [Although the OED isn't certain about this]
- The pubic hair (especially of a woman) and hence the female genitals. [Now scatological]
Each hair of her fud is the length of a span,Yes it is surprisingly little used given its scatological possibilities.
What fud can compare with the fud of Joan?
[Found in Mark Forsyth, The Horologicon]