I ALWAYS forget the oh-so-important two-letter words when I play but whenever I look online for a decent list, there are dozens of conflicting reports on what is appropriate. So this is my complied list of acceptable words for American tournament play approved by the National Scrabble Association. The words in bold are words also acceptable in the United Kingdom and in most Commonwealth countries.

AA AB AD AE AG AH AI AL AM AN AR AS AT AW AX AY
BA BE BI BO BY
CH
DA
DE DO
EA ED EE EF EH EL EM EN ER ES ET EX
FA FY
GI
GO GU
HA HE HI HM HO
ID IF IN IO IS IT
JO
KA KO KY
LA LI LO
MA ME MI MM MO MU MY
NA NE NO NU NY
OB
OD OE OF OH OI OM ON OO OP OR OS OU OW OX OY
PA PE PH PI PO
QI

RE
SH SI SO ST
TA TE TI TO
UG UH UM UN UP UR US UT
WE WO
XI XU
YA YE YO YU
ZO