Where does “монахъ” come from?

монахъ (Old Church Slavonic) comes from Ancient Greek μοναχός, from Ancient Greek μόνος, from Ancient Greek σπέρμα, from Proto-Hellenic *spérmə.

Ancestry of “монахъ”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	μοναχός	solitary, single; monk, monastic
2	Ancient Greek	μόνος	alone, forsaken, solitary; only; unique
3	Ancient Greek	σπέρμα	seed; semen, sperm; seed-time, sowing
4	Proto-Hellenic	*spérmə	—