Why is this compound named resorcinol?
For resorcinol, the naming is covered in a footnote to the Wikipedia article: 


  "Wir nennen den neuen Körper, da wir gefunden haben, dass er auch aus dem Ammoniakgummiharz erhalten werden kann, Resorcin, um an seine Entstehung aus Harzen und seine Beziehung zum Orcin zu erinnern." (We name the new substance, since we've found that it can be obtained from ammoniated resin gum, resorcin, in order to recall its creation from resin and its relation to orcin [i.e., orcinol].)


Which is itself a quote from  H. Hlasiwetz and L. Barth (1864) "Ueber einen neuen, dem Orcin homologen Körper", Annalen der Chemie, 130 (3) : 354-359.

At some point the ending -ol got added, to reflect the alcohol moieties in the compound.

Then name orcinol itself is derived from its association with orcein, a dye substance derived from orchil lichens.