The Spanish word 'sillón' (meaning 'armchair') has its roots in the Latin verb 'sedere' meaning 'to sit'. This evolved into the Latin word 'sedla' meaning 'seat', which then transformed into 'sella' meaning 'chair' in Latin. The Spanish word 'silla' (chair) comes directly from Latin 'sella', and 'sillón' is formed by adding the Spanish augmentative suffix '-ón' to 'silla'. The augmentative suffix '-ón' indicates something larger or more substantial than the base word, so 'sillón' literally means 'big chair' or 'armchair'.

This etymology shows how the concept of sitting evolved from a verb to various types of seating furniture, with the size distinction being made in Spanish through the use of the augmentative suffix.

The most obvious related Spanish word is 'silla' (chair), which is the base word from which 'sillón' is derived. While 'silla' refers to a regular chair, 'sillón' specifically denotes a larger, more comfortable armchair. Understanding this relationship helps remember that 'sillón' is essentially a 'big silla'.

While not immediately obvious, the English words 'sedentary' and 'seat' are distant relatives of 'sillón', as they also derive from the Latin 'sedere' (to sit). 'Sedentary' maintains the connection to sitting by referring to a lifestyle involving a lot of sitting and little physical activity. The word 'seat' evolved from the same root and maintains the basic meaning of a place to sit.