RATIONALE

Fundamental principle (9)

Solution has appeared in 2 crosswords (2 across and 0 down):

• Quick crossword No 16,210 — 2022-04-20 23:00:38
  22A: Logical basis for a course of action (9)
• Quick crossword No 15,901 — 2021-04-23 23:00:21
  20A: Fundamental principle (9)