Answer:

psi

Answer	Crossword Clue
PSI	Greek character
PSI	23rd Greek letter
PSI	Bike-tire letters

PSI	Greek letter
PSI	Omega predecessor
PSI	Pressure meas.
PSI	Tire letters
PSI	Chi follower
PSI	Pressure amount
PSI	Air indicator
PSI	Trident-shaped letter

PSI	Trident-shaped letter, in Rome
PSI	Air pump fig.
PSI	Penultimate letter of the Greek alphabet
PSI	Letter before omega
PSI	Letter after chi
PSI	Measure of inflation?
PSI	Omega proceder
PSI	Tire-air meas.

PSI	ESP, e.g.
PSI	Tire-pressure meas.
PSI	Extrasensory event
PSI	Of paranormal stuff
PSI	Omega preceder
PSI	Tire meas.
PSI	Next-to-last letter
PSI	Tire-pressure abbr.

PSI	Letter resembling a trident
PSI	114-Across's power
PSI	Air pressure unit
PSI	National fraternity Phi Kappa ...
PSI	Omega's predecessor
PSI	Penultimate letter in Paros
PSI	Final Greek consonant
PSI	Parapsychology term

PSI	Unworldly power
PSI	Frat-row fork
PSI	Penultimate Greek letter
PSI	Abbr. on a tire
PSI	Pitchfork-shaped letter