In ancient Greece the symbolon was a token of identity, a coin
with an image on it, that was broken in two parts, so your identity could
be verified by comparing its other half.
This comes from from sym 'to throw' and ballein 'together'.
So symballein was to put the two parts together, and if they matched you knew the identity of the bearer of the symbolon was for real.
In the 15th century the Greek symbolon, evolved into the Late Latin symbolum, a token, sign, or symbol.
So words are symbols, as are nodes, that suggest something else by reason of relationship, or of association, or convention. But words need both the meaning that the author attempts to convey, as well as the meaning that is in the readers mind.
When the two are the same, the symbol was effective in communicating the intent of the author.