The Spanish word 'pulgarcito' (meaning 'little thumb' or 'Tom Thumb') comes from combining the Spanish word 'pulgar' (meaning 'thumb') with the diminutive suffix '-cito'. The word 'pulgar' itself can be traced back to Latin, where it evolved from 'pollicaris' meaning 'of the thumb', which in turn came from the Latin word 'pollex' meaning 'thumb'.

The diminutive suffix '-cito' is commonly used in Spanish to indicate smallness or endearment, and when added to 'pulgar', it creates the meaning of 'little thumb'. This word is famously used in Spanish as the title for the fairy tale character known in English as 'Tom Thumb' ('Pulgarcito').

The most obvious related Spanish word is 'pulgar' (thumb), which is the base word from which 'pulgarcito' is derived. Understanding this connection helps remember that 'pulgarcito' literally means 'little thumb'.

While English doesn't have any common words directly related to 'pulgarcito' through the Latin 'pollex', we do use the term 'pollical' in medical and anatomical contexts to refer to things relating to the thumb. The word 'pollex' itself is still used in scientific terminology as the technical term for the thumb.