one
Isthmus, island
Allotment.
The mono word that means a bloc of one stone is monolith. The definition of monolith is a large block or single piece of stone.
According to dictionary.com, there does not appear to be a single word that means "by default".
Portion?
If you men single as in not married, then the word would be virgin
Focus
The Latin equivalent of 'sweet piece' is dulcis pars. In the word-by-word translation, the adjective 'dulcis' means 'sweet'. The noun 'pars' means 'piece'.
a piece of armour
flexibly
The answer is slip!!
A single word would be 'origin'.