The Spanish word 'testicular' comes from the Latin word 'testiculus', which was formed by combining 'testis' (meaning 'witness') with the diminutive suffix '-culus'. Interestingly, the Latin word 'testis' originally meant 'witness' - the anatomical meaning developed because testicles were considered 'witnesses' of virility in ancient Roman legal contexts. The Spanish word was formed by adding the adjective suffix '-ar' to 'testículo'.

This etymology might seem unusual, but it reflects how ancient Roman legal and cultural practices influenced the development of anatomical terminology. The transformation from 'witness' to an anatomical term is a fascinating example of how word meanings can change dramatically over time.

The Spanish word 'testículo' (testicle) is directly related to 'testicular' and is more commonly used. Another related word is 'testigo' (witness), which preserves the original Latin meaning of 'testis' and is frequently used in legal contexts.

English speakers will recognize related words like 'testicle', 'testicular', and 'testify'. While 'testicle' and 'testicular' share the anatomical meaning with Spanish, 'testify' (meaning to bear witness) retains the original Latin meaning of 'testis'. The word 'testimony' is another related term that preserves this connection to witnessing or providing evidence.