The French word 'diner' (to dine) comes from Popular Latin *disjējūnāre (to stop fasting).

The word lost three of its syllables. This strong degree of erosion can be seen in many French words.

Click the video below to hear how eight words eroded on their way to French.

On my Patreon, I explain how the Latin words changed so much in French, discussing the perfectly regular sound shifts that, for example, turned *aetāticum into 'âge'. 800 words; link in bio.