This is a rare Irish surname. It is in fact so rare that the famous dictionary of surnames for Ireland barely mentions it at all. Its rareness is perhaps not surprising given that the name probably means 'The hostage'. The origination is from the ancient pre 10th century Gaelic word 'giall' of which the usual meaning is hostage, although it is difficult to conceive of circumstances where a hostage would be the leader or chief of a clan. However in this respect it is often said that all Irish surnames are effectively nicknames, most of which refer to some particular physical aspect of the original chief. This is often personal as in the name Kennedy which means 'ugly head', so on this basis 'hostage', if for some reason the chief had been a hostage, may make some logical sense. The identity and dating of this original chief is lost in the mists of time, indeed there are few enough recordings of the surname as it is. All that is known is that today the nameholders are mostly to be found in County Leitrim, although there is some suggestion that they may have originated further west, perhaps in Sligo or Galway. A relevant recording is that of John Geelan, the son of James Geelan, who was christened at Mohill, in County Leitrim, on April 18th 1865.