The Spanish verb 'acusar' (to accuse) comes from the Latin verb 'accusare', which had the same meaning. The Latin word was formed by combining two elements: the prefix 'ad-' meaning 'toward' and the noun 'causa' meaning 'cause' or 'reason'. When these elements merged, the 'd' in 'ad-' assimilated to the 'c' in 'causa', giving us 'accusare'. The literal sense was something like 'to call (someone) to account' or 'to bring cause against (someone)'.

The word maintained its form and meaning quite consistently as it evolved from Latin to Spanish, with just the typical sound changes that occurred as Latin developed into Spanish, including the loss of the final '-re' from the infinitive form.

The Spanish word 'causa' (cause, reason) is directly related to 'acusar' since they share the Latin root 'causa'. While 'causa' maintains the basic meaning of 'reason' or 'cause', 'acusar' developed the more specific legal sense of bringing a cause against someone. Another related Spanish word is 'causar' (to cause), which is a simpler and more commonly encountered verb that shares the same root.

English speakers can easily remember 'acusar' by connecting it to the English word 'accuse', which comes from the same Latin source 'accusare'. The words 'cause' and 'because' are also related, coming from Latin 'causa'. This family of words has maintained similar meanings across both languages, making it easier for English speakers to understand and remember 'acusar'.