The OED uses a lot of abbreviations. Here's a guide that explains what they mean: https://public.oed.com/how-to-use-the-oed/abbreviations/
A librarian at Texas State University has created an entire Research Guide dedicated to using the OED. It's very helpful--just remember that you'll need to access the OED through the WVU site, so links in the TSU guide may not work: https://guides.library.txstate.edu/c.php?g=184334&p=1219511
