1. phone, operator, top up (I hope this word won't be too difficult; I couldn't think of anything else to start with)
2. game, round, items
3. white, orange, striped (I initially wanted a different word, but it turned out to be vulgar)
4. round, black, weapon
It will be tough for you, Ryabeta, very tough :)
I tried to choose more complex, or rather, not easy words :)
P.S. Hommy, why are you so cheeky? :)
Added 5 minutes later
by the way, is it necessary for all the listed words to be related to each other? They just need to all relate to the secret word).