sturdy [ME] ‘Reckless, violent’ and ‘rebellious, obstinate’ as well as ‘bold, strongly built’ were the early meanings of sturdy, which comes from Old French esturdi ‘stunned or dazed’ and in modern use ‘feather-brained’. There is a possibility that this is based on Latin turdus ‘a thrush’, a bird that used to be associated with drunkenness, probably because it was once common to see thrushes tottering around unsteadily after eating partly fermented grapes—there is a French expression soûl comme une grive, which means ‘drunk as a thrush’. There are instances from the 15th century onwards of references to a parasitic sheep brain disease called sturdy which made sheep dizzy and hare-brained, which could be a link.