Several dictionaries and thesaurii are available for the Scots language e.g. The Concise Scots Dictionary, edited by Mairi Robinson and first published by Aberdeen University Press in 1985. A revised edition of 820 pages was published in 1987.
A companion volume in many ways to the above work is The Scots Thesaurus edited by Iseabail Macleod and published by Aberdeen University Press in 1990 (536) pages. This presents much of the vocabulary given in the dictionary in a different form, subject-by-subject under a wide variety of categories such as "farming", "life cycle, family", "food and drink" etc. Each category is further subdivided into many topics, thus providing easy access to vocabulary for all sorts of situations.
For a dictionary for the Gaelic language, see A pronouncing and etymological dictionary of the Gaelic language by Malcolm MacLennan, published by Acair (613 pages) with ISBN 0-08-025713-5 (Hbk) and 0-08-025712-7 (Pbk). For more information on the Scottish Gaelic language see Gaelic and Gaelic Culture or check out some of the many links available on the web pages of the Gaelic-medium college Sabhal Mor Ostaig on Skye.
A Glossary of Archaic Scots Terms, as well as a number of modern Scots words and phrases useful for genealogical research, including legal terms and words linked to property and possessions which might be found in wills and testaments.
There is an online Dictionary of the Scots Language. This is an electronic version of the multi-volume publications Dictionary of the Older Scottish Tongue (DOST) and the Scottish National Dictionary (SND).
Another useful online resource with information on printed versions of the above dictionaries is provided by Scottish Language Dictionaries Ltd (SLD). Its website says "Scottish Language Dictionaries (SLD) aims in particular to develop Scottish lexicography, building on the achievements of the Dictionary of the Older Scottish Tongue (DOST) and the Scottish National Dictionary Association (SNDA)."