Relating to or resembling gallows; worthy of execution; brave or fearless to the point of being reckless.
From gallows (an execution structure) plus the adjectival suffix -ous, meaning 'having the quality or nature of the gallows,' or sometimes influenced by an old sense of 'gallant' or 'bold.'
The word 'gallous' is dying out in modern English, but old folk songs used it to describe outlaws as 'gallous fellows'—meaning they were so bold or so doomed that they seemed destined for the gallows.
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