✅ — but wait, GRIT has 4 letters. Unless the clue’s pattern is (4,2,3,4) or the first word is a 5-letter synonym.

Thus, the clue is a trick:

Given time constraints, the most likely answer for “useful material or knowledge” as a is:

If "Grist to the mill" doesn't fit your specific grid, the compiler might be looking for other terms related to useful knowledge, such as: (6) Lore (4) Data (4) Practical Wisdom (9, 6)