1. A stone that remains in one’s boot or shoe, despite unlacing, removing footwear, shaking out all unwanted contents, straightening socks, replacing said footwear, relacing and setting off one’s walk again.
2. as plural ‘nullocks’ the expletive used on discovering one’s footwear contains a nullock despite unlacing etc. Commonly heard on the shingle shores of the Suffolk coast.
Nullocks! That nullocking nullock is still in my nullocking boot.