The Spanish verb 'deber' (meaning 'to owe' or 'must') comes from the Latin verb 'debere', which had the same meaning of 'to owe' or 'to be obligated'. The Latin 'debere' developed from an earlier form 'dehibere' meaning 'to have from another', which was formed by combining two elements: the prefix 'de-' (meaning 'away from' or expressing privation) and the verb 'habere' (meaning 'to have'). The literal sense was thus 'to have something away from someone else', which evolved to mean 'to owe' - when you owe something, you have something that in a sense belongs to another person.

The Spanish verb 'haber' (meaning 'to have' as an auxiliary verb) is related to 'deber' as they both derive from Latin 'habere'. While 'haber' developed directly from 'habere', 'deber' took on its meaning of obligation through the addition of the 'de-' prefix.

Several English words are related to 'deber' through the Latin root 'debere'. The most obvious ones are 'debt' and 'debit', which retain the core meaning of owing something. The word 'due' is also related, coming from the same Latin source, and maintains the sense of obligation. Even the word 'duty' is a distant cousin, derived from Latin 'debere' through Old French.