Scrolling through a Monday-style grid, I notice 'decay' usually keeps it simple: short, clean fills like ROT or ROTS. I like puzzles that treat the word literally — fruit goes bad, wood rots — and the clue mirrors that with plain verbs or nouns. In my experience, early-week New York Times clues will often read something like "go bad" or "putrefy" and lead you straight to ROT, ROTS, SPOIL, or SPOILAGE, depending on the crossing letters and tense the constructor needs. Those three-letter slots are gold for constructors because they’re so flexible and familiar to solvers.
Later in the week, though, the constructors get clever. "Decay" might be clued as a physics-y term — think ALPHA or BETA when it's specifically about radioactive decay — or as part of a phrase, like 'exponential decline' hinting at HALF-LIFE. Sometimes you’ll see thematic misdirection: a clue that reads like a biology prompt actually wants "TOOTH" (as in tooth decay) or a cultural twist that points to a song or movie lyric where decay is metaphorical. I love trying to guess whether I'm looking at a literal spoilage clue or a more abstract, thematic use — it changes how I fish for crossings and which synonyms float to the top of my mind.