To comparison-shop is to go from shop to shop — or site to site — looking at the same kind of thing and checking the price, so you can buy the cheaper one. In American English it is a verb you can tense: “We comparison-shopped for a fridge.” Many people know the idea better as the noun comparison shopping. It can feel a little business-like; you can do it in real shops or online. Though actually it is not only for big buys — people comparison-shop for phone plans and toothpaste too — but the word shows up most when the price gap is worth the extra looking.