The word 'teat' has a direct and ancient lineage, originating from the Old French 'tete', which itself derived from the Frankish or other Germanic languages. Its ultimate source is the Proto-Germanic 'titt-', a base for words related to the breast or nipple, which is also the ancestor of the modern German 'Zitze'. This Proto-Germanic root is traced back to the Proto-Indo-European 'dʰeh₁(y)-', meaning 'to suckle'. The word's journey reflects a stable core meaning, moving from a child's term into standard English while retaining its fundamental reference to the anatomical or functional part used for nursing.

This is a simplex word of Germanic origin. It functions as a single, unanalyzable morpheme in modern English.