frendo.

Uncertain. Perhaps from Proto-Indo-European *gʷʰrendʰ- (“to crush; gnash”), cognate with Proto-Germanic *grindaną (“to grind”). Another plausible cognate is Lithuanian grę́sti (“to plane, scour”), but this requires an alternative root ending in *-d-. More information Sihler considers the development of *gʷʰr- to Latin fr- in this word surprising since a labiovelar consonant was generally delabialized in Latin when followed by another consonant (e.g. *gʷréh₂us > gravis). However, Sihler notes that the cluster *-gʷʰr- also retained its labialization in medial position, judging by the form of Latin febris from *dʰegʷʰ-. A separate cause of doubt is comparison with *gʰr- and *gʰl-, which are hypothesized to have developed into gr- and gl- in some Latin words, such as glaber. However, examples such as glaber are rare, and their precise cause is disputed. Weiss 2018 argues that the g- in glaber was caused by a process of aspirate dissimilation that can be dated after a change from *-ndʰ- to *-nd- in Proto-Italic: this chronology would prevent dissimilation from applying to the root *gʷʰrendʰ-.