gladi

A small domestic verb with a big frequency. Gladi is to run a hot iron over cloth. It is transitive and takes the thing being smoothed: gladi ĉemizon, gladi la tukojn. ReVo defines it in one word, glatigi - to make smooth - and that is exactly what the machine does.

The payoff is the tool. -Il- is the instrument suffix, so a gladilo is an iron: the thing itself, named as the smoothing-tool. You have met the pattern already in tranĉilo a knife, ŝlosilo a key, kombilo a comb and, four ranks after this one, balailo a broom. Then gladtabulo is the ironing board (gladtabulo or glada tabulo, both are used), gladisto and gladistino are people who iron for a living, gladado is ironing as an activity, and negladenda - un-iron-need-ing - is the wonderful one-word Esperanto for non-iron or wrinkle-free. Six useful words off one root, and you assemble every one of them yourself.

A near-miss worth naming. Gladi and glata (smooth) mean almost the same thing and look like a pair, but they are separate roots in Esperanto: glad- and glat-, one letter apart, both from the same Germanic family a long way back. Glatigi and gladi are therefore near synonyms rather than the same word taken twice, and only gladi implies heat and cloth. You can glatigi your hair or a sheet of paper; you cannot gladi either.

The figurative use exists and is mild. As in English, you can iron out a difficulty: gladi la malfacilaĵojn. Gogol's Revizoro in Esperanto has a character gladi his beard flat under his tie, which is the sort of thing the verb does happily.