Sake is the benefit or purpose of something, in the phrase for the sake of. For your sake, for the sake of argument, for goodness sake.
It survives only in that construction. For the sake of argument introduces a supposition nobody is committing to. For goodness sake and for heaven's sake are exclamations of exasperation, and the apostrophe in them is optional and much argued over. Note that sake once meant a lawsuit or dispute, which is why forsake means to abandon a cause.
1nounsakeThe benefit or purpose of something.
“Please be quiet, for the sake of the baby.”
sake is a purpose or benefit.
Old English sacu meant a lawsuit, cause or dispute. For his sake meant on his side in a case, and forsake and the German Sache come from the same matter.
Proto-Indo-European
*seh₂g- — to investigate
Proto-Germanic
*sakō — affair, thing, charge, accusation, matter
Proto-West Germanic
*saku
Old English
sacu — cause, lawsuit, legal action, complaint, issue, dispute
Middle English
sake — sake, cause
English, today
sake
From Middle English sake (“sake, cause”), from Old English sacu (“cause, lawsuit, legal action, complaint, issue, dispute”), from Proto-West Germanic saku, from Proto-Germanic sakō (“affair, thing, charge, accusation, matter”), from Proto-Indo-European seh₂g- (“to investigate”). Akin to West Frisian saak (“cause; business”), Low German Saak, Dutch zaak (“matter; cause; business”), German Sache (“thing; matter; cause; legal cause”), Danish sag, Norwegian Bokmål, Norwegian Nynorsk and Swedish sak, Gothic 𐍃𐌰𐌺𐌾𐍉 (“dispute, argument”), Old English sōcn (“inquiry, prosecution”), Old English sēcan (“to seek”). More at soke, soken, seek.
Etymology from Wiktionary, CC BY-SA