How about axle? Many tolls are based on the number of axles on a car.
toll
Unit. A four letter word beginning with the letter 'u' is unit. Also used, uvea, urea, Utah
boll till toil told
knot
GRAM
Unit
kilo
dyne
unit
unit
The four-letter word that U is pronounced like a short I is "unit." You're welcome.
room, hole, unit, ring