There is no inverse of oe_edit_only in Odoo 7.0


But if you really needs to do that then you need to edit in css file 

append this to in base.css file

.openerp .oe_form_editable .oe_save_only, .openerp .oe_form_editable .oe_form_field:empty {
  display: none !important;
}

then use class oe_save_only exactly like you use oe_edit_only

Hope This will Help :)

Please, could someone explain to me how to add a class to a field.i tried it but it shows me an XML architecture error.do i have to do something before using it?Thank you

Couldnt post a multiline comment so here is your solution @Soukaina SBITTI:

                <form string="Test" version="7.0">
                        <field name="a"/>
                        <field name="b"/>
                        <field name="c" class="oe_edit_only"/>
                </form>