Greek Grammar

Those ending in -yx, which are naturally long in the penultimate syllable, and those that are expressed with two consonants, are declined through -k. However, phryx Phrygian is declined through -g, such as phrygos.
Ho bōx. tou bōkos. Ho ptōx beggar. tou ptōkos.
Those ending in -ōx that are simple decline through -k, except for rhōx chasm/cleft, rhōgos.

A woodcut-style illustration depicts a Cyclops with the label: "The Cyclops, of the Cyclops."

Ho mōlōps weal/welt. tou mōlōpos. Ho gyps vulture. tou gypos.
Those ending in -ps decline through -p, except for araps Arabian, arabos; chalyps steel, chalybos; lips south-west wind, libos; kinyps a kind of insect, kinyphos; Pelops. Ho alkman Alcman. tou alkmanos.

Those ending in -an that are oxytonized accented on the final syllable are declined by the addition of -os. Ho Hellēn Greek. tou Hellēnos. Ho poimēn shepherd.

For those ending in -ēn: if they are oxytone and do not have -m-, they are declined by the addition of -os, such as sōlēn pipe/channel, sōlēnos, except for auchēn neck, auchēnos. Those that have -m- before the -ēn, such as -e-, decline as poimēn, poimenos, except for mēn month, mēnos. Those that are barytone and monosyllabic keep the -ē- in the genitive, such as Hellēn, Hellēnos. Those that have the second -e- are declined through -enos.