The Spanish verb 'fastidiar' (to annoy) comes from the Latin verb 'fastidiare' meaning 'to feel disgust or loathe.' This Latin verb was derived from 'fastidium' (disgust, aversion), which was formed by combining two Latin words: 'fastus' (pride, arrogance) and 'taedium' (weariness, disgust). The evolution shows how the concept moved from a combination of pride and weariness to a general sense of causing annoyance or irritation in modern Spanish.

A closely related Spanish word is 'fastidio', which means 'annoyance' or 'nuisance.' Both 'fastidio' and 'fastidiar' come from the same Latin root 'fastidium.' While 'fastidio' is the noun form describing the state or feeling of annoyance, 'fastidiar' is the verb form meaning 'to annoy' or 'to bother.'

The English word 'tedious' is etymologically related to 'fastidiar' through the Latin word 'taedium.' While 'fastidiar' developed to mean 'to annoy' in Spanish, the English descendant 'tedious' retained more of the original sense of 'weariness' from 'taedium,' coming to mean 'tiresome' or 'boring.' This connection can help English speakers remember that something or someone who is 'fastidioso' (annoying) often causes the same kind of wearying feeling as something tedious.