Yes, DEPENDENCY is a Scrabble word!

Letter values in Scrabble US: D 2, E 1, P 3, E 1, N 1, D 2, E 1, N 1, C 3, Y 4.

Is it a valid word?

DEPENDENCY is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

the state of relying on or being controlled by someone or something else
being abnormally tolerant to and dependent on something that is psychologically or physically habit-forming (especially alcohol or narcotic drugs)
a geographical area politically controlled by a distant country