NME and Sounds reputedly took the term Gothic from Siouxsie Sioux (of the 
Banshees) who used it to describe the new direction for her band. However 
the earliest significant usage of the term (as applied to music) was by 
Anthony H. Wilson who was overcome by a rare moment of lucidity on a
1978 BBC TV program when he described Joy Division as Gothic compared 
with the pop mainstream. Perhaps Joy Division (who he was managing) are 
not what we now think of as Goth but it is possible that they are at the 
source of the term. Bauhaus were labelled as Gothic as early as 1979 when 
they released Bela Lugosi's Dead. 

The pop journalists were quick to latch onto the term and they applied it 
in a nasty sort of pigeonholing way to a number of bands that were around 
in the early 80s - most of which did not sound much like the Banshees (or 
anyone else for that matter), the journalists were more concerned with 
looks. The (Southern Death) Cult was foremost amongst these bands,  like 
the Banshees they wore lots of black and silver and had extreme black 
hair. The Sisters of Mercy were also so labelled and when they split and 
Wayne Hussey founded the Mission they carried their label with them,
despite being different musically. Finally The Fields of the Nephilim 
appeared and they (perhaps) consciously and deliberately got themselves 
labelled as Gothic despite looking and sounding quite different to what 
had previously been labelled Goth.