The answer is SEXIVALENT
The corresponding square is house puzzle
   by Brian Tivol and Roger Barkan

The spiral can almost be completed as usual, except five of the
squares have two letters in them.  (Like, the TN for BEA(TN)IK and
KI(TN)A.)  These doubled squares all line up, and can be read in order
to spell the answer.

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Here's the answers to the clues:

 inward
   1-4    Confident				SURE
   5-11   Sedimentary agglomerate		BRECCIA
   12-19  At any point				SOMETIME
   20-28  Monopoly's theme			REAL(ES)TATE
   29-34  Dolt					NIMROD
   35-38  She played Bailey's sister		NEVE
   39-46  Without dissent			UNITEDLY
   47-50  Base					RAD(IX)
   51-54  Bo Derek flick			ORCA
   55-59  Caused				LEDTO
   60-64  Tenet					DOGMA
   65-73  Jenny father James			HARGRE(AV)ES
   74-78  Traveler's portmanteau		MOTEL
   79-85  Canadian violin troupe		BARRAGE
   86-94  Poison used in mysteries		B(EL)LADONNA
   95-100 Social unconventionalist		BEA(TN)IK
 
 outward
   100-97 He passes to Warrick			KI(TN)A
   96-93  Abba follower				EBAN
   92-88  Stable during vibrations		NODAL
   87-85  Czech river				(EL)BE
   84-81  Academy Award nominee for Tootsie	GARR
   80-77  Competent				ABLE
   76-69  By 98.84%, a baseball Hall of Famer	TOMSE(AV)ER
   68-63  _Post_ publisher Katherine		GRAHAM
   62-58  "Zap gun" Buck			GODOT
   57-50  Last great artist of the Renaissance, as per Baudelaire
						DELACRO(IX)
   49-45  1985 android matinee			DARYL
   44-38  Unlawful custody of chattel		DETINUE
   37-32  Cart pusher				VENDOR
   31-26  Member of Bush's Cabinet		MINETA
   25-22  Gigagamma				T(ES)LA
   21-15  Religious loner			EREMITE
   14-9   Web browser				MOSAIC
   8-1    Guard of Dante's third circle		CERBERUS