The building blocks of English

Affixes

-er4

Forming verbs.

Old English ‑erian, ‑rian, of Germanic origin.

Such verbs have an idea about them of repeated action: batter, clamber, flicker, flitter, flutter, glitter, shimmer, shiver, shudder. Some are imitative of a noise: blatter, chatter, clatter, mutter, splutter, twitter.