The Spanish verb 'enfermar' (to become sick) comes from the Latin verb 'infirmare' meaning 'to weaken or make sick.' This Latin verb was derived from the adjective 'infirmus' meaning 'weak or sick,' which itself was formed by combining the negative prefix 'in-' with the Latin adjective 'firmus' meaning 'firm or strong.' So etymologically, to be sick (enfermar) literally meant to be 'not strong' or 'not firm.'

Several common Spanish words share this etymology with 'enfermar': The adjective 'enfermo' means 'sick,' the noun 'enfermedad' means 'sickness/disease,' and 'enfermería' means 'infirmary/nursing.' All these words preserve the core meaning of 'not being strong' or 'being in a weakened state.'

The English word 'infirm' is directly related to 'enfermar,' coming from the same Latin root 'infirmus.' We can also see this connection in the English word 'infirmary' (a place for sick people) and 'firm' (strong, solid). The negative prefix 'in-' works the same way in both languages to create the meaning of 'not strong' or 'weak.'