Can anyone comment on the mutual derivation of cuideachd and cuideachail, please - also/too and helpful don't seem particularly related words, though the Gaelic does seem to be. Tapadh leibh.
I don't know about word derivations, but there is an interesting dictionary online called Am Faclair Beag at www.faclair.com.
If you look at it on a laptop/desktop and enter a word, there are two columns. The left column is labeled Faclair Beag Results and the right hand column is labeled Dwelly Results. If the dictionary opens in Gaelic, there is an option/link to use the English version.
The Dwelly Results are an online version of the "Illustrated Gaelic to English Dictionary" compiled and published by Edward Dwelly around 1910-1920.
Below are the entries I found for cuideachd (noun), cuideachd (adverb), and cuideachdail. I think there are some similarities in the long definitions given.
cuideachd -an, sf ind Troop, company, throng. 2 Society, intercourse.3 Friends, relations, 4** Private company. 'Nam chuideachd, in my company; cuideachd shaighdearan, a company of soldiers; a chuideachd a' chridhe, my dear people; bheir e e fhéin as gach cuideachd le ceòl is le conaltradh, he would acquit himself well in any company in music or conversation; ged a tha e math 'ga thoirt fhéin &c. tha e motha is math 'ga chuir fhéin ann, though he can acquit himself well in company, he is better at getting himself invited — he is too forward or cheeky; chan ann de mo chuideachd thù, you are not of my flock — an imitation of the cooing of a pigeon.
cuideachd adv Also, likewise. 2 Together, in company. 3 In contact. Thàinig esan cuideachd, he came too; cuideachd rium, along with me; theann i an lomairt cuideachd, she squeezed the fleece together.
cuideachdail -e, a Social, entertaining, sociable. 2 Assistant, helpful. 3(MS) Humourous.
Tapadh leibh. Interesting reading, and I should have thought to refer to Am Faclair Beag, I use it all the time, but admittedly for rather more basic stuff, like genders and plurals. I've even got a Dwelly on my bookshelves, from before it went on-line, I reckon. Thanks again for your trouble.