late Middle English: via Old French from Latin tortuosus, from tortus 'twisting, a twist', from Latin torquere 'to twist'
The two words tortuous and torturous have different core meanings. Tortuous means ‘full of twists and turns’, as in a tortuous route. Torturous means ‘involving or causing torture’, as in a torturous five days of fitness training. In extended senses, however, tortuous is used to mean ‘excessively lengthy and complex’ and hence may become indistinguishable from torturous: something which is tortuous is often also torturous, as in a tortuous piece of bureaucratic language; their way had been tortuous and very difficult. The overlap in sense has led to tortuous being sometimes used interchangeably with torturous, as in he would at last draw in a tortuous gasp of air.