Gaelic-English dictionaries & meanings in Gaelic
An Stòr-dàta Briathrachais Gàidhlig
The School Gaelic Dictionary
(Am Briathrachan Beag) by Patrick MacFarlane (1912) or online
version (shorter) & another version
Gaelic vocabulary for parents
dictionary
of political terms (Faclair na Pàrlamaid), Scottish government
dictionary of faun & flora Gaelic-English
resources: thematic dictionaries
Etymological dictionary
of the Gaelic language by Alexander MacBain (1911) or online version
(shorter)
Dictionary of the Gaelic language by Norman MacLeod
& Daniel Dewar (1909) 
Pronouncing
Gaelic dictionary by Neil MacAlpine (1833)
Vocabulary English and Gaelic by Patrick
MacFarlane (1815)
Guide to Gaelic conversation and pronunciation
& vocabularies, dialogues, phrases, and letter forms, by Lachlan MacBean (1905) or online
version
Gaelic vocabulary and phrase book by James Munro
(end 19th)
The tourists hand-book of Gaelic and English phrases
for the Highlands, by Mary Mackeller (1880) or online
version
Scottish land-names, their origin
and meaning, by Herbert Maxwell (1894)
A collection of Gaelic proverbs, and familiar phrases
with an English translation, by Donald MacIntosh (1785)
Gaelic course & Gaelic-English vocabulary
pronunciation (with sound)
basic grammar of Gaelic language
pronunciation (phonetic)
Gaelic course (bbc):
basic vocabulary (with sound)
A Gaelic grammar, principles
of phonology and etymology & proper and place names, by George Calder (1923)
Elementary course of Gaelic by Duncan Reid & Norman
MacLeod (1913)
How to learn Gaelic, orthographical
instructions, grammar, and reading lessons, by Alexander Macbain & John Whyte (1906)
Elements of Gaelic Grammar by
Cameron Gillies, based on the work of Alexander Stewart (1896)
Elements of Gaelic Grammar by Alexander Stewart
(1886)
A practical grammar of the Scottish Gaelic by James
Munro (1843)
books about Scottish Gaelic language: Google
books & Internet
archive
resources about Gaelic language
The Scotsman: in Gaelic or in English
(newspaper)
An Gàidheal Ùr [PDF] monthly
Radio nan Gàidheal (BBC) > listen
Carmina Gadelica (Gaelic songs): hymns, songs, collected
by Alexander Carmichael, in Gaelic & translation in English
Popular Tales
of the West Highlands collected by John Francis Campbell (1860) in Gaelic & translation in English: I & II
- III - IV
Tiomnadh Nuadh: New Testament in Gaelic
(1813)
Gospel of Mark in Gaelic, multilingual text
Tha gach uile dhuine air a bhreth saor agus co-ionnan ann an urram 's ann an còirichean.
Tha iad air am breth le reusan is le cogais agus mar sin bu chòir dhaibh a bhith beò nam measg fhein ann an spiorad bràthaireil.
Scotland: maps, symbols, heritage & documents
Irish Gaelic language & Manx Gaelic language
Celtic languages (in French)
Scots language: language of the Lowlands