-t-

Etymology 1
From the -t of, which survived in Old French in some verb forms, now still spelt with -t (such as etc.). In Middle French, when final was no longer pronounced outside of liaison, the ending was reinstated analogically in the inversion forms of all verbs, even those in which -t had already been lost in Old French (such as those from  > ).

Note, however, that verbs spelled with final -t, -d can make liaison generally before a vowel, while the others do so in inversion only.

Etymology 2
A 'euphonic' consonant added before certain vowel-initial suffixes (such as the verb-forming suffix ) in order to prevent a hiatus when deriving new words from a base that ends in a vowel. It might be influenced by the use of /t/ as a liaison consonant. Although avoided in this context, hiatus is phonologically possible; it occurs in words that were not derived within French by suffixation (e.g., borrowed from Latin ) and some suffixed words such as , show hiatus (or a realization of the first vowel as a semivowel).

When the base ends in a nasal vowel, the inserted consonant sound is sometimes /n/ instead, with denasalization of the preceding vowel; there are many examples from bases ending in -on /ɔ̃/ (compare also ), some from bases ending in -an /ɑ̃/ or -en /ɛ̃/. However, /t/ can also be used after bases ending in a nasal vowel; often ones spelled with final -nt (as in ), but sometimes after bases spelled with final -n (as in.

Sometimes, as the result of analogy, another unetymological consonant is inserted before a vowel-initial suffix upon derivation (not necessarily after a vowel); e.g. /d/ after /ɑ̃/ in, or after /aʁ/ (due to the influence of words ending in ) in , ,.

Interfix

 * biffeton, dépiauter, gruter, maintée
 * biffeton, dépiauter, gruter, maintée
 * biffeton, dépiauter, gruter, maintée

Etymology
Euphonic linking sound.

Interfix

 * + -t- + →
 * + -t- + →
 * + -t- + →