[This is part of a series of defectivity case studies.]

Morin (1987:33f.), cited in Boyé & Cabredo Hofherr (2010), draws attention to the French verb frire ‘to fry’. It is unobjectionable in the present active singular—je fris, tu fris, il frit—but apparently defective in the plural; according to my informants, speakers paraphrase this using inflected forms of faire frire ‘to make fried’. Arrivé (1987), also cited by Boyé & Cabredo Hofherr, lists frire and about a dozen other verbs as defective; according to my informants, all are rare, archaic, or unfamiliar.

Consider the case of frire briefly. It has an obvious analogical model: rire ‘to laugh’, which suggests *nous frions ‘we fry’, and so on. One obvious possibility is that this is somehow in competition with *nous frissons (cf. je finis/nous finissons ‘I/we finish’ and most 2nd conjugation verbs), which would give rise to a weird homophony with the plural of frisson ‘shiver; excitement’.¹

Endnotes

1. Here the ss appearing in the plural is ultimately descended from the Latin inchoative infix -sc- as seen in, e.g., nascō ‘I am born’. Neat, right?

References

Arrivé, M. 1997. La conjugaison pour tous. Hatier.
Boyé, G., and Cabredo Hofherr, P. 2010. Defectivity as stem suppletion in French and Spanish verbs. In Defective Paradigms: Missing Forms and What They Tell Us, ed. M. Baerman, G. G. Corbett, and D. Brown, 35–52. Oxford University Press.
Morin, Y.-C. 1987. Remarques sur l’organisation de la flexion des verbes français. ITL Review of Applied Linguistics 77-78: 13-91.