while it is possible to achieve what you want using CSS and/or javascript it's not a wise approach and I do not recommend it.

icons are just visual triggers to the functions granted to a user. the same function is possible to invoke several different ways from several different places.  if you hide an icon from the user at one place, it doesn't mean you restrict a user to perform it some other way.

I would rather recommend to revoke user's permissions that you think user shouldn't have available.

Hi Leah Giambartolomei‌,

Marian Hatala is correct since the users would be able to delete the forms from the list view. You will be able to disable the delete using the following approach with SharePoint permission levels:

1. Navigate to Site Settings > SIte Permissions > Permission Levels
   
   
   
   
2. Open up the Permission Level that most closely represents the Permission Level you are trying to achieve and create  a copy. Provide a name, then remove the Delete Items capability and Submit.
   
   
3. Navigate to List Settings > Permissions for this list
   
   
4. If List is inheriting from the parent site, break permissions by selecting Stop Inheriting (unless they shouldn't be able to delete anything from the site in which case you should assign the permissions there).
5. Add the User or Group to the item permissions and assign the new permission level restricting delete. Make sure they don't exist in the other groups (or adjust the group permissions also).
   
   

When the users access the forms, they will not be able to select Delete.

Let me know if you have any questions!

Scott Carnegie

Thank you so much for your help! How do I make a copy of a permission level?

If you open the permission level you wish to duplicate, at the bottom you will find the Copy Permission Level button.

Scott

Dear Leah Giambartolomei‌, 

If you need to disable the delete button from the ribbon by using user's permissions, be aware of the below:

1-You are removing the delete permission from the user.

In any related Workflow, you will not be able to delete any item from the list unless you will go to the "Set Permission" action or any alternatives...

2-Using JavaScript will be a good option if you don't want to customize the permission levels. The draw back of the client side option is that a good developer can re-enable the delete button from the browser development console.

Cheers...  

Thank you Scott. I do not have those buttons on my permission levels. I am not sure why I do not see them. 

still trying to figure it out! 

Thank you for the heads up. I think that it is okay in this case for the general user to not be able to delete.

Hi Leah,

Check out this link:

How to create and edit Permission Levels - SharePoint 

To create or make changes to permission levels, you must belong to a SharePoint group that includes the permission to Manage Permissions. By default, you have this permission if you belong to the Owners group or if you are a Site Collection Administrator.

Are you a Site Collection Administrator or Owner?

That is the strange part...I am both a Site Collection Admin and Owner... 

Hi Leah,

I believe the permissions levels must be created on the root site of the Site Collection. If you open up a permission level from the root site, you should be able to see those buttons!

Yes I was able to get this to work! I was not on the root site. Such a silly mistake. But I successfully was able to copy one of the permission levels and save it as a new one without the delete option. This removed the delete option from the ribbon as well. Thanks for your help!

@lgiambar You can now just hide the Edit button from the ribbon without needing to mess with permissions and such. 

This will stil work on Nintex Responsive Forms that don't have the CSS Custom option.
Check it out here: https://community.nintex.com/t5/Nintex-for-Office-365/Is-there-still-custom-CSS-and-Javascript-in-new-Responsive/m-p/105772/highlight/true#M12290