The story
- Middle English · derived fromgalstren“to make a noise or outcry”
- English todaygosther
The OED suggests derivation from Middle English galstren (“to make a noise or outcry”) (found only in the Ancrene Riwle), but the Middle English Dictionary glosses this same word as "to stink". Compare Middle Low German galstern (“demand shamelessly”), Old High German galstar (“chanting, crowing, an incantation”).
Etymology from Wiktionary, CC BY-SA 4.0.