The Spanish verb 'abonar' comes from combining the Latin prefix 'ad-' meaning 'toward' with the Latin word 'bonus' meaning 'good', plus the Spanish verb suffix '-ar'. The prefix 'ad-' changed to 'ab-' when combined with 'bonus'. The literal construction means something like 'to make toward good' or 'to make good', which evolved into meanings like 'to pay' or 'to vouch for' in modern Spanish.

Some related Spanish words include 'bueno' (good), which comes from the same Latin root 'bonus', and 'abono' (fertilizer, payment), which is directly related to 'abonar'. The connection between these words makes sense when you think about how fertilizer makes soil 'good' for plants, and how paying what you owe makes your account 'good'.

English speakers might recognize the Latin root 'bonus' in words like 'bonus' (extra good thing), 'bonify' (to make good), and 'boon' (a good thing, a benefit). The word 'bounty' also comes from this same Latin root, showing how the idea of 'goodness' evolved into concepts of generosity and abundance.