The Spanish word 'bonito' has two distinct etymologies depending on whether it's used as an adjective meaning 'pretty' or as a noun referring to a type of fish.

As an adjective meaning 'pretty', 'bonito' comes from combining the Spanish word 'bueno' ('good') with the diminutive suffix '-ito'. The word 'bueno' itself derives from Latin 'bonus' ('good'), which evolved from an earlier Latin form 'duonus' meaning 'efficient, good'.

As a noun referring to a type of fish, 'bonito' comes from Late Latin 'boniton', which specifically referred to this species of fish.

The most obvious related Spanish word is 'bueno' meaning 'good', which is one of the first words Spanish learners encounter. While 'bueno' refers to something generally good, its diminutive form 'bonito' evolved to specifically mean 'pretty' or 'nice-looking'. This semantic shift from 'good' to 'pretty' through the use of the diminutive '-ito' suffix shows how Spanish often uses diminutives to add nuance and soften meanings.

The English word 'bonus' comes from the same Latin root 'bonus' meaning 'good'. While Spanish 'bonito' developed to mean 'pretty' through the addition of a diminutive suffix, English 'bonus' maintained the meaning of something extra or good that is given as a reward or benefit. The English word 'bounty' also comes from this same Latin root, referring to generosity or abundance of good things.