Barter: "Definition coming sooon." Yes, the linked source really used three "o"s to spell "soon".
Capital: "Commodity-Money-Commodity"..."the circulation
of money as capital
is an end in itself"
Money: "...a material
embodiment of abstract and therefore equal human labour."
Marxism, the Left, exists as a counterpoint to Capitalism. It is the shadow to Capitalism's sunlight.
By Marxist definition, Capital (and Capitalism) cannot exist outside of a "money" environment. A corollary is that Marxism cannot exist outside the "money economy" For example, Marxism is meaningless in the "family economy" because the family does not rely on money-based transactions.
By Marxist's own definition, Money is abstract. By Marxist's own definition, "Social Capital", "Character Equity", "Skills as Capital", "Intellectual Property" and "Fertile Land as Capital" are oxymorons. Nor are the tools needed to produce a Glock 19 or an iPhone 6 considered "Capital". "Capital" can only be "Money", entries in a ledger book, somewhere.
Production is treated as a natural force by Marxists, much like gravity or the tides. The allocation of profit is all that Marxists are concerned about. Production, like the tides, is not influenced by the allocation of "profit"...at least in the Leftist's mind. And in the very short term they might be correct. But in the longer term.....
The Left can only rule when there is surplus that subsidizes their abstract universe. Their policies inevitably eat the seed corn. Surplus declines. The Left fades. The pragmatic ascend. Results matter. Surplus increases. Envy is stoked. The Left ascends.
Lather. Rinse. Repeat.