Unknown. Related to Karelian tehaš. The modern sense is first attested in Carl Helenius: Suomalainen ja ruozalainen sanakirja ("Finnish and Swedish Dictionary", 1838), while in the folk language, the word had a variety of (regionally varying) meanings, including "cow stall" (mainly Savonia and North Karelia, but also parts of Tavastia and Ladoga Karelia), "plant bed" (parts of Tavastia and Satakunta) and "leg room for a boat rower" (Northern Finland). Theories include: * tehdä (“to do, make”) + -as, but the -d- is unaccounted for (the stem of tehdä is teke-). In addition, -as generally forms adjectives, not nouns (albeit some nouns are also known, e.g. opas). The modern sense "factory" is probably also recent and probably inspired by tehdä, even if this is not the origin ot the word. * Sometimes considered a borrowing from Proto-Germanic *stihtiz, *stihtaz (“footprint, step (in stairs), rung”), but the semantic shift is unlikely. LÄGLOS rejects this theory. * More recently, it has been suggested that the word, alongside teho (dialectal tehto), derives from an Indo-European borrowing, probably akin to Proto-Indo-European *dʰeh₁- (whence also possibly Proto-Uralic *teke- > tehdä).