The Spanish verb 'acojonar' meaning 'to frighten or intimidate' is formed from three parts: the prefix 'a-', the noun 'cojón' (meaning 'testicle'), and the verbal suffix '-ar'. The noun 'cojón' comes from Latin 'coleo', also meaning 'testicle'. The prefix 'a-' is commonly used in Spanish to form verbs, while '-ar' is the standard infinitive ending for many Spanish verbs.

The semantic development from 'testicle' to 'frighten/intimidate' reflects a vulgar slang evolution where losing or affecting one's testicles became metaphorically associated with losing courage or being intimidated. This type of semantic development is common in many languages where body parts become associated with emotional or psychological states.

The most directly related Spanish word is the more common noun 'cojón' (testicle), which is considered vulgar slang. You might also encounter the adjective 'cojonudo' (meaning 'awesome' or 'amazing' in colloquial speech) and the similar verb 'descojonar(se)' (to break down laughing). All these words share the same Latin root and demonstrate how a basic anatomical term developed various colloquial and emotional meanings in modern Spanish.

While there aren't any commonly used English words directly related to 'acojonar', the Latin root that gave us 'coleo' is related to the English medical term 'coleus' (referring to the scrotum or testicular region). However, this term is primarily used in medical contexts and is not common in everyday English.