Oxford English Dictionary (which I access via Harvard)
All Things Linguistic (Gretchen McCulloch)
Semantic Scholar ("A free, AI-powered research tool for scientific literature")
JSTOR (which I access via Harvard)
World Wide Words ("Investigating the English language across the globe")
A Way With Words (podcast)
Current British English pronunciation dictionary ("searchable transcriptions")
Glosbe Dictionary: All Languages of the World in One Place
Phrases And Sayings, With Meanings And Origins Explained phrases.org.uk
Idioms and phrases thefreedictionary.com
The Phrase Finder Library of Congress
OneLook Thesaurus and Reverse Dictionary Inbox onelook.com
Unlimited AI Word Finder AI Phrase Finder.com
I am of two minds about Google. On the one hand, ever since it first appeared I've used it as a primary tool for locating relevant items, but on the other hand, I am wary of its "AI" and user-management/extraction sides. Google Scholar ("Stand on the shoulders of giants") and Google Books ("the world's most comprehensive index of full-text books.") and Google Books Ngram Viewer are all indispensable tools for my enterprises.