Starch
Old English (recorded only in the past participle sterced ‘stiffened’), of Germanic origin; related to Dutch sterken, German stärken ‘strengthen’, also to stark.
wiktionary
From Middle English starche, sterche, from Old English *stierċe(“stiffness, rigidity, strength”), from Proto-West Germanic *starkī(“stiffness, rigidity, fortitude, strength”), ultimately from Proto-Indo-European *sterg-(“stiff, rigid”). Cognate with dialectal Dutch sterk(“starch”), Middle Low German sterke(“strength”), German Stärke(“strength", also "starch”), Swedish stärkelse(“starch”), Icelandic sterkja(“starch”). Related to English stark(“stiff, strong, vigorous, powerful”).
etymonline
starch (v.)
late 14c., from Old English *stercan (Mercian), *stiercan (West Saxon) "make rigid," found in stercedferhð "fixed, hard, resolute" (related to stearc "stiff"), from Proto-Germanic *starkjan "to make hard" (source also of German Stärke "strength, starch," Swedish stärka "to starch"), from PIE root *ster- (1) "stiff." Related: Starched; starching.
starch (n.)
"pasty substance used to stiffen cloth," mid-15c., back-formation from starch (v.). Figurative sense of "stiffness of manner" is recorded from 1705.
