inverse element
element with an inverse with respect to a given mathematical operation; element that can 'undo' the effect of another given element
en-US/ˌɪnˈvɝs ˈɛləmənt/
en-GB/ˈɪnvɜːs ˈɛlɪmənt/
element with an inverse with respect to a given mathematical operation; element that can 'undo' the effect of another given element