The Spanish word 'infante' comes from the Latin word 'infans', which literally meant 'unable to speak' or 'young child'. This Latin word was formed by combining two parts: the prefix 'in-' meaning 'not' and 'fans' meaning 'speaking'. So literally, an 'infans' was 'one who does not speak', referring to a baby or very young child. In Spanish, 'infante' evolved to mean not only 'infant' but also came to be used as a title for children of the royal family, particularly princes who were not the firstborn (similar to how English uses 'infant' for a baby).

Some related Spanish words include 'infantil' (childish or infantile) and 'infancia' (childhood). These words maintain the connection to the original meaning of young children or early developmental stages.

The English word 'infant' comes from the same Latin root 'infans'. Other related English words include 'infantry' (originally meaning a group of young, junior soldiers who served on foot), 'infantile' (childish), and 'infancy' (early childhood). All these words preserve the connection to youth or the early stages of development.