Letter appearing only in down answers; its opposite appears only in across answers

Question:

Answer:

HARDG

Length:

Similar Crossword Questions:

Number of times the letter 'U' appears in each of this puzzle's eight longest answers
Word appearing in all nine theme answers
Struck out, as one letter in each of this puzzle's theme answers
Item hidden in each of the 15-letter answers in this puzzle
Three-letter combinations hidden in this puzzle's six other longest answers
Triatomic gas in a thinning layer ... and, symbolically, what appears in this puzzle's four longest answers
What three-letter words do in five answers in this puzzle
Angle irons graphically represented by four sets of black squares in this grid, and by letter formations starting in the four 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)
Groundbreaking sitcom, and a hint to four different three-letter words concealed by starred answers
Country that skips every other letter in the starred answers
HBO hit, or a hint to the starts of this puzzle's 11-letter answers
Metaphor for kinetic grace ... or what this puzzle's six eight-letter answers display?
Letter that begins and ends this puzzle's six longest answers
Bit of footwear that appears at both ends of this puzzle's theme answers
A type of one appears in each part of this puzzle's longest answers
Last letter in most plurals (but not in this puzzle's six longest answers, which are the only plurals in this grid)
New element whose name will be ratified in January, 2010, and whose symbol appears in the middle of this puzzle's theme answers
"Fiddler on the Roof" setting that answers the question "Where else could Sabbath be so sweet?"
Some Winslow Homer art ... or what five answers in this puzzle are?
Answers of acceptance
Sunday dinner that's "mixed up" in four answers
What five answers in this puzzle are
The 2x2 black square near the middle of this puzzle's grid, e.g., which is part of eight answers
"Dog the Bounty Hunter" network, and a hint to the theme in this puzzle's four longest answers