'mood-lowering' originates from Modern English as a compound of 'mood' and the present participle 'lowering'. 'mood' itself comes from Old English 'mōd', meaning 'mind, spirit, temper', while 'lowering' is derived from the verb 'lower' (a Middle English development ultimately from Old English roots) meaning 'to make lower or less high'.

'mood' evolved from Old English 'mōd' into Middle English and then Modern English with a sustained sense of 'mind/spirit/temper'. The verb 'lower' developed through Middle English (forms such as lowren/lowen) into the modern verb 'lower', and the present participle 'lowering' produced compounds like 'mood-lowering' in contemporary usage.

Initially the components meant 'mind/spirit' (mood) and 'to make lower' (lower); when combined in Modern English the compound has been used straightforwardly to mean 'causing a decline in mood' or 'depressing'.