Speak too soon, say

The answer to the crossword question “Speak too soon, say is ERR” is the word “Jump.” The phrase “speak too soon” refers to someone who prematurely makes a declaration or assumption. The word “say” is a clue to form a noun meaning, and the noun for making a mistake is “err.” The hint is indicating that the word should be interpreted in the opposite way, where “jump” means a sudden action or decision made without any hesitation or deliberation. Therefore, the answer to the crossword question is “jump,” which means to act without thinking.