tightest

closely constrained or constricted or constricting;
pulled or drawn tight;
set so close together as to be invulnerable to penetration;
pressed tightly together;
(used of persons or behavior) characterized by or indicative of lack of generosity;
affected by scarcity and expensive to borrow;
of such close construction as to be impermeable;
of textiles;
securely or solidly fixed in place; rigid;
(of a contest or contestants) evenly matched;
very drunk
exasperatingly difficult to handle or circumvent;
demanding strict attention to rules and procedures;
packed closely together;

tightest is a valid Scrabble (US) TWL word

tightest is a valid Scrabble Word in Merriam-Webster MW Dictionary

tightest is a valid Scrabble Word in International Collins CSW Dictionary

tightest is a valid Words With Friends word