Here are some possibilities:
Meaning: Uneven, odd, irregular:
* सम (sam): Even, regular, smooth
* समान (samaan): Equal, alike
* नियमित (niyamit): Regular, consistent
Meaning: Difficult, tough, challenging:
* सुगम (sugam): Easy, simple
* सरल (saral): Easy, simple
* आसान (asaan): Easy
Meaning: Odd, strange, unusual:
* सामान्य (saamaan): Common, ordinary, normal
* सामान्य (saamaan): Usual, typical
* प्राकृतिक (prakritik): Natural
Meaning: Dangerous, risky, hazardous:
* सुरक्षित (surakshit): Safe, secure
* निर्जल (nirjal): Safe, harmless
* असुरक्षित (asurakshit): Safe, secure
To give you a more precise opposite, please provide the context in which you are using the word "visham".