Glen Quoich is a quiet glen in the eastern Cairngorms running from Strath Dee at Allanaquoich to the foot of Beinn Bòrd.
As a place name Glen Quoich is obscure – the most widely accepted derivation is 'of the cup', but this derivation assumes the name is from Cuaich - meaning cup, and further assumes that's a reference to the Punch Bowl at Linn of Quoich.
The 'of the cup' derivation is given in Watson (1975), but not in Watson & Allan (1984) - from that I infer that expert opinion is backing away from that derivation. The reason appears to be 'obvious' - the spellings of 'Quoich' in the old estate papers and maps is similar, but still varies widely enough for any conclusion about the derivation to be highly speculative.
Whatever the derivation of Quoich - the river running through the glen is Uisge Quoich. The source of the river is in the Invercauld Forest on the north-east plateau of Beinn Bòrd between the North Top and Cnap a' Chléirich, where it is named An t-Allt Dearg. The burn drops quickly through Coire nan Clach, and almost due east of the big tor of Beinn Bòrd named A' Chìoch it is joined by An Glas Allt Mór from the north-east. The burn then turns towards the south-west around the bottom of Coire na Cìche where it is joined by Allt Coire na Cìche from the north-west. A short distance further on - after a 'zig' to the south-east, and a 'zag' to the south-west it crosses into Mar Forest.
The old name of this area of Invercauld Forest was Caich - frequently appearing in the papers of Invercauld referred to as the Forest of Caich. The place name survived the 19th century appearing in Robertson (1822) as a label applied to the burn - the old 6-inch map (1869) as a label 'Ciach Lodge' applied to the shooting lodge at the south-east edge of the area - and into the early 20th century as a written reference to the shooting lodge in (smcj 43, January 1904, p47).
In Mar the glen is named Am Beitheachan, and there's no doubt the upstream area in Invercauld was considered well enough defined to deserve a name too. That leads neatly to my own speculation on the derivation. With the little knowledge of Gaelic I have - the derivation seems obvious. The big tor on Beinn Bòrd named A' Chìoch - meaning the breast, is too obvious a landmark for it not to have be used as a reference for the area, and just I can't imagine not using 'of the breast' as a reference for the area.