From "subscribe" and sharing its definition. Originally derived from an unintentional typographical error on some deskbound cnut wishing to "un-dubdribe" from BEMLi
Corruption of 'subscribe'. Opposite of 'undubdibe' or 'unsubscribe'. Arose from the haste with which sensible, good natured people would attempt to depart the BEMLi causing inaccuracies in their typing.