The across clues can be solved to yield a valid crossword puzzle with words (including some abbreviations) going across and down. The down clues can be solved to yield a valid crossword puzzle with words going across and down, but mostly not the same words. They need to be solved as two separate puzzles with the same grid, as in the Siamese Twins crossword variety.
ORE ICK USES INS TSK MOPE ANN CAN ATOLL ROT WON TIBIA RAVIOLI DELVE SWAHILI WRENS IAN GRE VIP BUT GPA SEE STOP SHE JEST MILE THE NESS ABU ATTIRE ARE ESTATE CASTLE NATURE CASTLE COWARD SPLEEN NOG BITCHY SAO TAMP LAD KING TANS SAY KING ALA EAR PIT ATO GEL PEN KITES TRADING KATIE IMAGINE EBERT HOW NET ERECT CAW NEA SIDE YEN GEO SIDE OWN EDT
Six words are the same in both grids. In clue order, they spell CASTLE KING SIDE, KNIGHT TAKES PAWN, which is written as O-O, NxP in standard chess notation. OONXP is the answer to the puzzle.