gustumi

This is a real -um- word, and a good one to learn the suffix by. Gusto is the flavour a thing has. -Um- means "do the obvious related thing", the affix Zamenhof left deliberately vague, and gustumi is what you get when you apply the obvious action to a flavour: you take a small amount into your mouth on purpose to find out what it is like. The -um- article is worth reading alongside this one, because -um- is the only affix with no fixed meaning and it has to be learned word by word.

English "taste" hides two different verbs, and Esperanto separates them. Gustumi is the agentive one, with a person doing the tasting: la kuiristo gustumis la saŭcon. The other one, where the food is the subject, is gusti: la supo gustas sale, the soup tastes salty. Most word lists gloss gustumi simply as "to taste", which quietly invites the mistake. If a learner writes la supo gustumas bone they have said that the soup is going round sampling things.

Gustumado is tasting as an event, so a wine tasting is vingustumado, and gustumaĵo is a sample given out to be tasted.