verb/e.tʁɛ.ne/
to use/wear for the first time, to premiere; (of clothes) to break in; (figurative) to unveil, introduce; to be the guinea pig
“Les gamins, vêtus pareillement à leurs papas, semblaient incommodés par leurs habits neufs (beaucoup même étrennèrent ce jour-là la première paire de bottes de leur existence), […].” — The lads, dressed like their papas, seemed uncomfortable in their new clothes (many that day handselled their first pair of boots), […] .
From étrenne + -er.