If, like me, you don't want to give the users you support the opportunity to mistakenly (or mischievously) delete the list item whilst in the form interface, then this is for you.

Just insert the following script into the Custom CSS box of the Form Settings, before the other CSS already in there (so, it's easy to find):

On-Premise SharePoint 2013 Nintex Forms:

/*hide delete button in ribbon for Display form*/

#Ribbon.ListForm.Display.Manage-LargeMedium-1

{

display:none;

}

/*hide delete button in ribbon for Edit form*/

#Ribbon.ListForm.Edit.Actions.DeleteItem-Large

{

display:none;

}

SharePoint Online 365 Nintex Forms:

/*hide delete button in ribbon for Display form*/

#Div1

{

display:none;

}

/*hide delete button in ribbon for Edit form*/

#RibbonDeleteButton

{

display:none;

}

I got this using a bit of trial and error based on previous posts I've seen elsewhere. Hope it is useful for others, too.