Ah yes, the first wild Opsday of Ops Week, traditional Opalia (the Women's Movement counter to Saturnalia) dedicated to reckless entertainment... as if the Guff needed any additional excuse for madness. Ops, wife of Saturn, Earth Goddess of Plenty (she gave her name to "opulent") in whose honor one touched earth instead of wood for luck, gave earthenware gifts, and fraternized regardless of rank or clout.
This is almost right. The fertility goddess Ops got her name from Proto-Indo-European *h₃ep- "to work, produce in abundance". This PIE root is also the source of opulent (the suffix -ulentus meaning "abounding in, full of").
The root became Latin operārī "to work" (as in opera, operate). Post-classical Latin manu operari "to perform manual labour as a feudal service" became Anglo-Norman mainoverer "to work or till land". This was borrowed into English as manure "to till or cultivate". This was soon used for "dung, excrement, compost" as spread over or mixed with soil to fertilize it. (OED) Also related is maneuver.
The Old English derivative efnan "to work" became the northern English eem "to spare time, to find and opportunity, to succeed (in doing a thing)"
1674 RAY N. Country Wds. Coll. 16 Chesh...I cannot Eem, I have no leisure, I cannot spare time.
Old English efnan "to throw down, to level" (English even) is unrelated.