Resembling, containing, or having the quality of gruel; thin, watery, and unappetizing, or exhausting like consuming gruel.
From 'gruel' (thin, meager porridge from Middle Dutch 'gruwel') plus the adjective suffix '-y', describing something that has the quality of gruel.
The word 'gruelly' is wonderfully descriptive—it combines both the literal (like actual thin porridge) and metaphorical (spiritually meager) senses, because eating gruel meant accepting deprivation!
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