To Feel Sad About a Missed Opportunity

This page is the CodyCross answer for the clue below from Space Exploration, Group 912, Puzzle 2 (Katherine Johnson).

Question is: To Feel Sad About a Missed Opportunity

and the answer is: REGRET

Word Meaning:

REGRET — To feel sorry about (a thing that has or has not happened), afterthink: to wish that a thing had not happened, that something else had happened instead.

Definitions from Wiktionary.