noun, masculine/lystʁ/plural: lustres
lustrum; period of five years; a very long time, an eternity
“Ça fait des lustres que je ne t'ai pas vu !” — I haven't seen you in ages!
Synonyms: éternité, plombes, belle lurette
Borrowed from Latin lūstrum (“purification celebrated every few years; a period of five or four years”).