Herculis 4d

[Plumbers]

Is it 'key'? If so, it doesn't fit with Apollo 9acr.

[johnalex]

Cay

[Y.Odinlim]

I'm no great linguist, and KM does come up with some obscure spellings occasionally, but I've a feeling that the right format might be Kay, rather than Cay. Check either of them on Google and you'll see what I mean...or just toss a coin.
After all it was KM who plumped for Skat (W.Indian), rather than the more correct jazz term of Scat, as spelled by both Satchmo and Ella, who were the originators of the term.
Anyway 50/50 is better than the odds of being the first out of the DTel hat, even if you do get it right!!
Good Luck.

[Plumbers]

Thanks johnalex! It was the last one i needed.

[Ont-ice]

From Chambers:
key2 or cay noun (keys or cays) a small low island or reef formed of sand, coral, rock or mud, especially one off the coast of Florida.
ETYMOLOGY: 17c: from Spanish cayo.