Loanwords
The majority of the vocabulary of Scottish Gaelic is native Celtic. There are a large number of borrowings from Latin, (muinntir, Didòmhnaich), ancient Greek, especially in the religious domain (eaglais, Bìoball from Ekklesia and Biblia), Norse (eilean, sgeir), Hebrew (Sàbaid, Aba), French (seòmar) and Lowland Scots (aidh, bramar).
In common with other Indo-European languages, the neologisms which are coined for modern concepts are typically based on Greek or Latin, although written in Gaelic orthography; television, for instance, becomes telebhisean and computer becomes coimpiùtar. Although native speakers frequently use an English word for which there is a perfectly good Gaelic equivalent, they will, without thinking, simply adopt the English word and use it, applying the rules of Gaelic grammar, as the situation requires. With verbs, for instance, they will simply add the verbal suffix (-eadh, or, in Lewis, -igeadh, as in, "Tha mi a' watcheadh (Lewis, "watchigeadh") an telly" (I am watching the television), instead of "Tha mi a' coimhead air an telebhisean". This was remarked upon by the minister who compiled the account covering the parish of Stornoway in the New Statistical Account of Scotland, published over 170 years ago. It has even gone so far as the verb Backdatigeadh. However, as Gaelic medium education grows in popularity, a newer generation of literate Gaels is becoming more familiar with modern Gaelic vocabulary.
Going in the other direction, Scottish Gaelic has influenced the Scots language and English, particularly Scottish Standard English. Loanwords include: whisky, slogan, brogue, jilt, clan, trousers, gob, as well as familiar elements of Scottish geography like ben (beinn), glen (gleann) and loch. Irish has also influenced Lowland Scots and English in Scotland, but it is not always easy to distinguish its influence from that of Scottish Gaelic. See List of English words of Scottish Gaelic origin
Source: MacBain, Alexander (2009: original pre-1923). An Etymological Dictionary of the Gaelic Language (Digitized facsimile ed.). BiblioBazaar. ISBN 978-1-116-77321-7.
There are also many Brythonic influences on Scottish Gaelic. Scottish Gaelic contains a number of apparently P-Celtic loanwords, but as there is a far greater overlap in terms of Celtic vocabulary, than with English, it is not always possible to disentangle P and Q Celtic words. However some common words such as monadh = Welsh mynydd Cumbric *monidh are particularly evident. Often the Brythonic influence on Scots Gaelic is indicated by considering the Irish Gaelic usage which is not likely to have been influenced so much by Brythonic. In particular, the word srath (Anglicised as "Strath") is a native Goidelic word, but its usage appears to have been modified by the Brythonic cognate ystrad whose meaning is slightly different.
Read more about this topic: Scottish Gaelic