The Spanish verb 'descontar' (to discount) is formed from two main parts: the prefix 'des-' (meaning negation or reversal) and the verb 'contar' (to count). The verb 'contar' itself comes from Latin 'computare' meaning 'to calculate', which was formed by combining the prefix 'com-' (meaning 'together, with') and the verb 'putare' (meaning 'to prune, reckon, or think'). The evolution from Latin 'computare' to Spanish 'contar' involved a simplification of the word structure, dropping the prefix 'com-' and evolving the root to a more Spanish-friendly form.

When the negative prefix 'des-' was added to 'contar', it created 'descontar', literally meaning 'to un-count' or 'to take away from a count', which developed into its modern meaning of 'to discount' or 'to deduct'.

The most obvious related Spanish word is the simpler and more common verb 'contar' (to count). This is the base verb from which 'descontar' is formed. Other related words in the same family include 'cuenta' (account, bill), 'contador' (accountant), and 'contable' (accountant, accounting).

English speakers can relate 'descontar' to several familiar English words that share the Latin root 'computare'. The most obvious ones are 'compute' and 'count'. The word 'account' also shares this origin, coming from Old French which got it from Latin. Even our modern word 'computer' is a descendant of this same Latin root. Notice how all these words relate to calculation or counting in some way.