'athyroidism' originates from Greek elements: the prefix 'a-' meaning 'without' and 'thyreoeidēs' (Greek for 'shield-like', the root for 'thyroid'), combined with the suffix '-ism' (state or condition) in New Latin/modern medical English.

'athyroidism' is a modern medical English formation derived from Greek roots (a- + thyreoeidēs) via New Latin medical coinages such as terms like 'athyreosis', and later standardized in English as 'athyroidism'.

Initially the components conveyed simply 'without thyroid' (absence of the gland); over time the term has been used both for anatomical absence and more broadly for absence or severe deficiency of thyroid function.