To yammer is to talk on loudly and complainingly. Yammering away, yammer about it, stop yammering.
It is dismissive: whoever uses it has stopped listening. The word once meant to lament, which is a serious thing, and it has come down in the world to mean noise. Note the Old English geomrian behind it.
1verbyammerTo talk on loudly and complainingly.
“The kids yammered on in the back of the car about being hungry and bored.”
yammer is a way of speaking.
Old English geomrian means to lament or mourn, from a Germanic root about misery. The sense weakened to mere noise.
Proto-Germanic
*jēmarōną — to show misery or sadness
Proto-West Germanic
*jāmarōn
Old English
ġeōmrian — to lament
Middle English
ȝameren
English, today
yammer
From Middle English ȝameren, ȝaumeren, yemeren, ȝomeren, from Old English ġeōmrian (“to lament”), from Proto-West Germanic jāmarōn, from Proto-Germanic jēmarōną (“to show misery or sadness”), from Proto-Germanic jēmaraz (“miserable, sorrowful, sad”), from Proto-Indo-European yem- (“to hold, match, defeat”). Reinforced by cognate Middle Dutch jammeren (modern Dutch jammeren), from the same ultimate origin. Cognate also with Scots yammer, stq jammerje, West Frisian jammerje, German Low German jammern, German jammern, Danish jamre, Norwegian jamre. Compare also Old Norse amra (“to howl, wail, yammer”).
Etymology from Wiktionary, CC BY-SA
Practised in A Song of Ice and Fire