A "wardrobe workhorse" refers to a piece of clothing or an accessory that is versatile and reliable. It's something you can depend on and wear frequently. Full definition
That EF boxy shell is a true wardrobe workhorse for me! (stylebee.ca)
These somewhat simple and versatile items are not to be underestimated because they can become wardrobe workhorses. (youlookfab.com)
Each season, legions of fans rely on the brand's chic - yet - practical separates, all of which can be worn year - round: luxe knits done in minimal earth - tones, slouchy suiting, and wardrobe workhorses punctuated with unexpected twists (a prim puff shoulder detail here, a nipped peplum - waist there). (shop.goop.com)