The SSKJ says: "ekspr., s širokim pomenskim obsegom izraža dejanje, ki je znano, a se no�?e, ne more imenovati" ("expr., with a broad semantic range expresses an action that one knows but does not want to or cannot name."
The SAS says: "to tamper (z with); to muck about (z with)."
I would add: "to fool around; play around; etc."
onegáv: "having a quality that one knows but does not want to or cannot name." (SSKJ)