Here are the possible solutions for triatomic gas in a thinning layer and symbolically what appears in this puzzle's four longest answers clue
Answer
Clue
Relevancy
ozone
Clue
Triatomic gas in a thinning layer ... and, symbolically, what appears in this puzzle's four longest answers
Definition
an allotropic form of oxygen present in the atmosphere
argon
Clue
Noble gas, and a homophonic hint to how this puzzle's four longest answers are formed
Definition
an inert gaseous element
four
Clue
Number of times the letter 'U' appears in each of this puzzle's eight longest answers
Number of times this puzzle's theme word appears diagonally in the grid (to complete the puzzle, shade those words plus the Down answers that begin where they meet)
Definition
the cardinal number next above three
house
Clue
A type of one appears in each part of this puzzle's longest answers
Definition
to reside in a building
saw
Clue
A kind of one appears in this puzzle's seven longest answers
nba
Clue
Org. that has four teams with non-plural nicknames, which begin this puzzle's four longest answers
lbars
Clue
Angle irons graphically represented by four sets of black squares in this grid, and by letter formations starting in the four longest answers
