The Spanish verb 'cansar' (to tire) has an interesting etymology that combines influences from both Latin and Greek. It derives from two Latin verbs that merged: 'quassare' meaning 'to shake or damage' and 'campsare' meaning 'to turn or double back'. The Latin 'campsare' itself comes from the Greek 'κάμπτειν' (kamptein) meaning 'to bend'.

The semantic evolution from these source words to the modern meaning of 'to tire' is quite logical: physical exhaustion can be understood as a kind of 'damage' or 'wearing down' (from 'quassare'), while the idea of 'bending' or 'turning back' (from 'campsare/κάμπτειν') evokes the image of someone buckling or slouching from fatigue.

The Spanish word 'cansancio' (tiredness, fatigue) is directly related to 'cansar'. Another related term is 'descansar' (to rest), which literally means 'to un-tire' or 'to remove tiredness', formed by adding the prefix 'des-' (meaning reversal or removal) to 'cansar'.

While there aren't direct English cognates from the same Latin roots, the Greek root 'κάμπτειν' (kamptein) meaning 'to bend' has given English some technical terms. For example, 'campylotropous' (describing a curved botanical structure) and 'camptodactyly' (a medical condition involving bent fingers). However, these are specialized terms that aren't commonly used in everyday English.