jack oak

noun

1

: blackjack sense 5

2

: an extremely variable oak (Quercus ellipsoidalis) of east central North America having leaves with sharply pointed lobes and ashy gray turbinate to goblet-shaped acorn cups with persistent dull pubescence

Love words?

You must — there are over 200,000 words in our free online dictionary, but you are looking for one that’s only in the Merriam-Webster Unabridged Dictionary.

Start your free trial today and get unlimited access to America's largest dictionary, with:

• More than 250,000 words that aren't in our free dictionary
• Expanded definitions, etymologies, and usage notes
• Advanced search features
• Ad free!