'nonfebrile' originates from Latin elements: the prefix 'non-' (from Latin 'non', meaning 'not') combined with 'febrile', which comes from Latin 'febrilis' related to 'febris' meaning 'fever'.

'febrilis' in Latin gave rise to English 'febrile' (via classical/medical Latin usage), and the modern English adjective 'nonfebrile' was formed by adding the negating prefix 'non-' to 'febrile' in Modern English.

Initially 'febrile' related to 'fever' (pertaining to fever); the addition of 'non-' created the negated sense 'not having fever', which is the current meaning of 'nonfebrile'.