It ain't easy to explain and im sure some teacher would explain better but here is my two cents: Karşı can have more than one meanings depending on the usage in a sentence for example if we say Mağaza evin karşısında it would mean the shop is across the house. It could also mean opposite if used as an adjective verb like ben buna karşıyım would mean im against it Tersi would mean the opposite or like the complete 180 revers :D Like if we say Dediğimizin tam tersini düşünüyor it would mean He/She thinks the opposite of what we say complete 180 contrary :P Karşıt would again mean opposite or contrary opposing if used as an adjective like Karşıt görüşler would mean opposing opinions. Karşıt could also be used like an anti- sense like İrkçılık karşıtı fikirler would mean antiracist ideas and such (God it is so hard to explain i hope you understand) Zıtlık would be used as a noun for contrast. Like İkisinin arasında bir zıtlık var would mean there is a contrast between the two. Aykırı would mean opposing or against if used as an adjective like aykırı fikirler would mean opposing ideas. Aykırı insanlar would mean people who are against each other and stuff. Dude i hope you understand something from the stuff i wrote and it wont make things worse it is the first time explaining some Turkish to a learner and probably the last cause it is so hard and complicated to explain. Enjoy and cheers!