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non-trivial
The word trivial means "useless". So a trivial set would be a useless set.
Speak to him about something trivial on his own not in a group and see if he speaks to you more than he would if in a group
Ask him for a small favour and see how quick he obliges :)
Smack, smuck or smuth all mean group of jellyfish.
I presume the Question refers to 'Mail On Sunday' Trivial Pursuit quiz, where the answer is SMACK.swarm
Trivial is an adjective.