-ed

From Middle English -ede, -ed. During the Middle English period, this increasingly standard -ed ending largely absorbed the class 1 weak past ending (-de) through morphological leveling. However, many class 1 verbs resisted this leveling to become modern irregular verbs (such as kept and left). This resistance was driven by phonotactics: attaching the consonant suffix directly to the stem often triggered pre-cluster vowel shortening (and consonant devoicing) in Early Middle English, creating a stark vowel alternation between the present and past tense that anchored the irregular form. Conversely, verbs that lacked this stark alternation (such as deem, where the early past tense demde remained insufficiently distinct from the present stem) were highly vulnerable to leveling, adopting the syllabic -ed to ensure the past tense was clearly marked. In modern usage, this morphological leveling has proceeded further in American English than in British English, which frequently preserves the irregular -t variant for such verbs.
Ultimately from Proto-Germanic *-ōd-. Cognate with Saterland Frisian -ede (“-ed”, first person singular past indicative ending), Low German -de (“-ed”, first and third person singular past indicative ending), Dutch -d (“-ed”), German -t (“-ed”), Swedish -ade (“-ed”), Icelandic -aði (“-ed”).

From Middle English -ed, from the merger of Old English -od (class 2 weak past participle) and -ed (class 1 weak past participle), ultimately from Proto-Germanic *-ōdaz and *-idaz respectively. Cognate with Saterland Frisian -ed.

From Middle English -ed, from Old English -od (adjective suffix), from Proto-Germanic *-ōdaz, from Proto-Indo-European *-eh₂tos. While identical in appearance to the past participle of class 2 weak verbs, this suffix was attached directly to nouns without any intervening verb. Cognate with Latin -ātus (whence also a doublet -ate), Proto-Slavic *-atъ.