The Prefix ξε- (“un- / off / de-”)
The prefix ξε- REVERSES or REMOVES - it is Greek’s “un-/de-/off-”. On a verb it undoes the base action: κλειδώνω (“I lock”, from κλειδί “key”) → ξεκλειδώνω (“I unlock”), and the reflexive κουράζομαι (“I get tired”) → ξεκουράζομαι (“I un-tire = I rest/relax”), whose noun ξεκούραση (“rest”) you already know. ξε- can also mean “thoroughly off/away” (ξεγράφω “I cross out / write off”). Contrast it sharply with ξανα-: ξανα- REPEATS the action (ξαναγράφω “write AGAIN”), while ξε- UNDOES or strips it (ξεκλειδώνω “UNlock”). Like ξανα-, ξε- is unstressed and the base verb keeps its own conjugation and stress: ξεκλειδώνω (present), ξεκλείδωσα (past). Reading a ξε- verb, look for the base underneath and read “un-” onto it: ξε- + κλειδώνω = “unlock”, ξε- + κουράζομαι = “rest”.
The rule
The prefix ξε- reverses or removes - it is Greek’s “un- / de- / off-”. On a verb it undoes the base action: κλειδώνω (“lock”, from κλειδί “key”) → ξεκλειδώνω (“unlock”), the reflexive κουράζομαι (“get tired”) → ξεκουράζομαι (“un-tire = rest”, whose noun ξεκούραση “rest” you know), and γράφω → ξεγράφω (“cross out, write off”). Hold it sharply apart from ξανα-: ξανα- repeats the action (ξαναγράφω “write again”), while ξε- undoes it (ξεκλειδώνω “unlock”). Like ξανα-, ξε- is unstressed and the base verb keeps its own conjugation and stress: present ξεκλειδώνω, past ξεκλείδωσα. Meeting a ξ- verb, decide first which prefix it is - the meaning flips between “again” and “un-”.