But Jews and Muslims are not allowed to describe themselves as 'Abrahamic'? In fact I would suggest that it is Christians that are not Abrahamic.
To me 'Abrahamic' refers to the convenant between God and Abraham: Genesis 17:10 This is my covenant, which ye shall keep, between me and you and thy seed after thee; Every man child among you shall be circumcised. 11 And ye shall circumcise the flesh of your foreskin; and it shall be a token of the covenant betwixt me and you....14 And the uncircumcised man child whose flesh of his foreskin is not circumcised, that soul shall be cut off from his people; he hath broken my covenant.
In this way most Christians opt out of the Abrahamic covernant. Abraham would not approve of this behaviour by most Christians who have broken his covernant with his God.