Is “Thirdly” a Scrabble word?
Yes
THIRDLY
Valid in at least one Scrabble dictionary
Valid in these dictionaries
SOWPODS / CSW
Scrabble UK & International
TWL / NWL
Scrabble North America
Large English Dictionary
General English word list
Meaning of Thirdly
/ˈθɜːdli/
adverb
1.In the third place; third in a row.
Synonyms: 3rdly