There are at least two possible derivations of the name. One being that Crook here refers to the cruik the hook on which cooking pots are suspended over open hearths. The second is that Crook is a corruption of cross - in this case possibly a wayside pilgrim's way marker.
The name Crook is possibly from the word Cruik. It is the Scot's word for the hook from which cooking-pots, gridles etc, were suspended. For more about this definition see the Dictionary of Scottish Language. This is not a new thought as it was put forward in the reprint of the Works of Alexander Pennecuik in 1815. The Cruik or Cruiks hung by chains from a rantle-tree which was a iron or wooden beam high in the lum (chimney) or from an iron Sway. The Sway was a hinged right angled bracket fixed to the side of the fireplace allowing the cooking pots to be swung forward away from the fire - the hearth being at or just above floor level. The sway could be quite short, say about a foot long for more usually were much longer - about three feet. A good example of a medium sized sway can be seen over the grate in the tearoom section of the Laurel Bank Tearoom/Bistro/Bar in Broughton. It is surprising how big the fire-places were in those days - even in small rooms, particularly if there was ingle-neuk seating and the chain hanging from the rantle-tree and the associated cruiks could be quite substantial. At the Crook Inn it would certainly have been a large fireplace with ingle-neuk seating with the rantle-tree method for suspending the cooking pots.
Religious origin - apart from the cruik/cooking pot origin of the name of Crook there is a nagging notion that the name could be older - much older - and of religious origin. This concept is also not new as Sir Herbert Maxwell writing in 1909 states - old wayside Inn of Crook, the name denoting the former site of a cross. In the thirteenth century the lands in the area including South Kingledores were held by the Monks of Melrose. It is recorded that there was a St. Cuthberts chapel, known as Chapel Kingledores, south of the Kingledores burn at this time that would only be a mile or so, as the crow flies, from the site of the Crook Inn. The Chapel site is noted by the RCAHMS on Canmore as ID49765. The Lands of Crook are mentioned in documents up to the present day and as discussed in the preamble in the charter of 1572, in connection with Kingledors, there is the mention of a Cruikburn. Just behind the Inn is a Crook Hill with Crook Head at the summit. These mentions of Crook/Cruik outwith any connection with the Inn itself does suggest that the Inn was named after the land on which it stood. How the land actually got this appellation is open to conjecture but there are several possibilities :-
a) From a wayside cross - Erected at the time of St. Cuthbert to signify the coming of Christianity to the area and provide a focal point for the locals to visit - no churches at this time. There would have been others in the area notably at the ford at Chapel Knowe.
b) Pilgrims's Way marker, continuation of a). We do know that there was a Pilgrim's Way through the valley due to the presence of the Tweeds Cross at the southern end of the Parish - this was also a boundary marker. The location of the Cruik Pilgrim's Way marker was stratagic as it was at the topographical dog-leg of the valley and the narrowing of the valley pinching the river Tweed and road and subsequent railway to a narrow defile. Polmood Castle was subsequently built at this point that provided the important relay of warning signal-fires down the valley.
c) Boundary marker, continuation of b). Marker for the southern boundary of the lands "leased" by Sir Simon Fraser of Oliver to the Monks of Melrose that we know included the St Cuthbert's chapel at South Kingledores.
d) From Chapel Kingledores itself. Kingledores Chapel is shown on Blaeu's map of 1654 below - also on the map is shown the Cruick - interestingly the word is written parallel with the Tweed and written over a burn - Cruikburn? This would appear to indicate that the word Cruik here is referring to the lands and not to the actual dot of the Crook Inn? The sites of both Oliver Castles are misplaced on this map.
It has has come to light is that the phrase Lands of Crook appears in legal documents up to the present day. In 1926 the Masterton brothers of Broughton bought the Lands of Crook, Nether Oliver and Fruid. The Lands of Crook must have stretched to Tweedsmuir as the Masterton gifted a plot of land part of the Lands of Crook for the construction of the Village Hall. Also it is noted that the field just east of Tweedsmuir Kirk, presently known as part of The Insch was known as Crookholme field. This would appear to indicate that the Lands of Crook stretched from Chapel Kingdedores to Chapel Knowe.
Although the Dictionary of the Scottish Language mentioned above does not list the word cruik as being a corruption of cross or having any religious connection at all I believe that this could be a very local exception. The Cruikburn is possibly what is now known as the Glenmore burn which is the present northern boundary of Tweedsmuir parish or possibly the Quilt Burn that is north of the Glenmore and nearer to Kingledores. There is a Crossburn at the southern end of the parish that is so named as it's source was at Tweeds Cross. The Glenmore Burn - Cruikburn - passes very close to the Crook Inn making it very nearly in Drumelzier parish and hence nearly in the lands of Kingledores. Prior to 1643 the whole area was part of Drumelzier parish and before that it was Stobo parish. Armstrong in 1775 noted that the "Crook is an inn on the second stage on the road to Moffat - A small cot-house within a few yards of the inn belongs to the parish of Drumelzier". Armstrong was keen on vestiges of chapels, wayside crosses etc but he makes no mention of Chapel Kingledores or of a wayside cross in his Peeblesshire narrative. For more about the chapel and St Cuthbert see the Chapel Knowe page.
It is of note that Armstrong mentioned that in Tweeddale that a cairn; a pile of stones on a hill-top were oftened termed Cairn, Pike, Currough. Cross etc.