grueling

The adjective 'grueling' emerged in the mid-19th century from the verb 'to gruel', meaning to exhaust or punish severely. This verb, in turn, derived from the noun 'gruel', referring to a thin, simple food often given as a punishment or to invalids. The semantic journey moved from a specific, unappealing substance to a metaphor for a punishing experience that drains one's strength, much like a sustained ordeal. Thus, the modern abstract meaning of an extremely demanding and exhausting task retains this core sense of a punishing trial.

The word is a simplex form derived from the verb 'gruel', meaning to exhaust or punish. The verb 'gruel' itself originates from the noun 'gruel' (a thin porridge), used metaphorically.