adverb/lɔ̃.tɑ̃/
for a long time; over a long period
“Ça fait longtemps que ton frère habite chez toi ?” — Has your brother been living at your place for a long time?
Related: avant longtemps, de longtemps
From long + temps, from Old French lonc tans. Ultimately inherited from Proto-Indo-European *dlongʰos, which is also where the English long time came from. The French term is a partial cognate, not a calque, of the English one.