Previously we played with the Australian reference, the Macquarie Dictionary. Subsequently, as an international family finding that an expensive and static resource insufficiently engaged with international usage we began to play admitting anything in either dictionary.com or wiktionary with an English entry, excepting proper names and non-naturalized acronyms. As official scrabble cheat words cover a lot of random Scots/Welsh, you might choose to permit those (single result page on Wiktionary). It starts to get ridiculous fast. I personally love the learning aspect and we do not play the traditional "challenge" rule, in fact we actively encourage consultation of reference works before and after each play. I am a big fan of Wiktionary, occasionally adding to existing English and Middle Chinese entries.
For example, according to Wiktionary, boid (and its plural) should be permitted under etymology two, ie. member of the family Boidae of non-venomous snakes or etymology three, ie. Nonstandard spelling of bird representing the New York City pronunciation. We would not permit it under etymology one (computer program name). Now look - you learned something! https://en.wiktionary.org/wiki/boid#English
For example, according to Wiktionary, boid (and its plural) should be permitted under etymology two, ie. member of the family Boidae of non-venomous snakes or etymology three, ie. Nonstandard spelling of bird representing the New York City pronunciation. We would not permit it under etymology one (computer program name). Now look - you learned something! https://en.wiktionary.org/wiki/boid#English