Mine was from the dictionary:
"a secret or illegal cooperation or conspiracy, especially in order to cheat or deceive others.
or
"illegal cooperation or conspiracy"
The Trump tower meeting clearly fits that definition. It was a secret meeting, as a result of people conspiring by email for the express purpose of cheating in the election (receiving valuable information from the Russian government as part of their effort to get Trump elected, in direct contradiction of the law banning the solicitation of anything of value from foreigners for a campaign). That's collusion. There are other examples, too, like Manafort colluding with Russian intelligence operative Kilimnik, including secretly sharing polling with him to get illegal help in the election:
https://www.cnn.com/2019/01/09/politics/paul-manafort-donald-trump-robert-mueller/index.html
So, since my definition clearly fits the fact patterns, you must be using some other definition of "collusion" when you claim there was none. What definition is that? Be specific, please.