Definitions Found:
ALPHA, a Greek letter
- TAUGreek letter shaped like a cross
- OMEGAGreek letter shaped like a horseshoe
- DELTAAirline whose name is a Greek letter
- GNUAnimal whose name sounds like a Greek letter
- PSIGreek letter spelled out at the start of a Beatles title?
- BETALetter after alpha
- ETASixth letter after alpha
- SIGMAGreek letter
- PSIGreek letter
- CHIGreek letter
- RHOGreek letter
- ETAGreek letter
- TAUGreek letter
- IOTAGreek letter
- PSIPenultimate Greek letter
- ZETASixth Greek letter
- ETASeventh Greek letter
- OMEGAFinal Greek letter
- PHI21st Greek letter
- OMEGALast Greek letter
- CHIGreek letter X
- IOTANinth Greek letter
- PSITrident-shaped Greek letter
- PSIGreek letter before omega
- PSIPitchfork-shaped Greek letter
- PSINext-to-last Greek letter
- DELTALetter in the Greek or NATO alphabet
- PHIGreek letter that represents the golden ratio
- THETAGreek letter traditionally associated with Earth Day
- PHIGreek letter associated with the 33-Across
- TAUGreek letter that once symbolized life and resurrection
- PHIGreek letter that's also an M.L.B. city on scoreboards
- EROSGreek god whose name is one letter off from 118-Down
- EOSGreek goddess whose name is one letter off from 69-Down
- ZETALetter that's not really at the end of the Greek alphabet