The Spanish verb 'asustar' (to frighten) has an interesting development from Latin roots. It comes from the Proto-Romance 'sustar' (to frighten), which itself developed from the Latin verb 'suscitare' meaning 'to raise up' or 'to excite.' The Latin 'suscitare' was formed by combining the prefix 'sub-' (meaning 'under') with the verb 'citare' (meaning 'to excite' or 'set in motion'). The modern Spanish form gained the prefix 'a-' (from Latin 'ad-' meaning 'to, toward'), which is a common prefix in Spanish verbs.

A related and simpler Spanish word is 'suscitar' which means 'to provoke' or 'to give rise to.' This word maintains a more direct connection to the original Latin 'suscitare' both in form and meaning, while 'asustar' evolved to specifically mean 'to frighten.'

English speakers might recognize the connection to words like 'excite' and 'incite,' which come from the same Latin root 'citare.' While these English words maintained meanings related to stirring up or stimulating action, the Spanish 'asustar' developed the more specific meaning of stirring up fear or fright.