δερμάτινη is the feminine singular form of the adjective, used before feminine singular nouns, and δερμάτινο is the neuter singular form of the adjective, used before neuter singular nouns. (Or the masculine accusative singular form used before a masculine singular noun in the accusative case.)
Ah, got it. Yes: the Greek keyboard maps phonetically to the U.S. English keyboard quite well where possible. The exceptions, like "c/ψ" and "v/ω", usually occur when there is no corresponding letter (no Greek "c", no English "ω"). You'll often find that you can indeed spell spell out the word, as in γάντι, σκύλος, πουκάμισο, etc.