This word is acceptable for play in the UK dictionary that is being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

n. The lower or posterior half of the theca of a thecate protist such as a diatom or dinoflagellate

n. An obligation by which property of a debtor was made over to his creditor in security of his debt.

n. The inner half of the frustule of a diatom.

"The substantial pledge has been refined into the invisible rights of a mortgage or _hypotheca_; and the agreement of sale, for a certain price, imputes from that moment the chances of gain or loss to the account of the purchaser."

hypothec   

hypothecal   

epitheca