Yes, SECRETARY is a Scrabble word!

Letter values in Scrabble US: S 1, E 1, C 3, R 1, E 1, T 1, A 1, R 1, Y 4.

Is it a valid word?

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

a person who is head of an administrative department of government
an assistant who handles correspondence and clerical work for a boss or an organization
a person to whom a secret is entrusted
a desk used for writing

Also: secretarial assistant, writing table.

Not playable in Scrabble US: SECRETAIRE.