Yes, LOUNGER is a Scrabble word!

Letter values in Scrabble US: L 1, O 1, U 1, N 1, G 2, E 1, R 1.

Is it a valid word?

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

someone who wastes time
an armchair whose back can be lowered and foot can be raised to allow the sitter to recline in it
an article of clothing designed for comfort and leisure wear

Also: dilly-dallier, reclining chair.

Not playable in Scrabble US: DILLYDALLIER.