I checked it out on Bartleby via Onelook. Here's the entry with lowdown shown as one word--hooray! You can use it in Scrabble!

lowdown

SYLLABICATION: low·down
PRONUNCIATION: ldoun
NOUN: Slang The whole truth: gave us the lowdown on what happened at the party.


Bartleby regards,
Dub

Edit and Addendum. MW has a slightly different take:

Main Entry: low·down
Pronunciation: 'lO-"daun
Function: noun
Date: 1915
: the inside facts : DOPE