'meno' (as a combining form) ultimately originates from Ancient Greek, specifically the word 'mēn' (μη̂ν) meaning 'month' (and by extension the monthly menstrual cycle); the musical term 'meno' comes from Italian 'meno' meaning 'less', from Latin 'minus'.

The combining form entered Late Latin/Modern scientific usage from Greek 'mēn' and appeared in medical Latin as 'meno-' in words like 'menopause' and 'menorrhagia'. The musical/colloquial 'meno' is from Italian 'meno' (from Latin 'minus') and entered English musical terminology through Italian score directions. Separately, the proper name 'Meno' is from ancient Greek personal names (Μένων/Meno).

Initially the Greek root meant 'month' (and related cyclical/menstrual senses); over time that sense specialized into a medical combining form in English (meno-) referring to menstruation or monthly cycles. The Italian 'meno' retained the sense 'less' and was adopted unchanged into musical directions.