Definitions of Allowable Two Letter Words

AA	rough jagged lava found in Hawaiian volcanos
AB	an abdominal muscle
AD	short form of advertisement
AE	one (Scots.)
AG	agricultural
AH	(verb) to say "Ah" for joy etc
AI	a three-toed South American sloth
AL	an East Indian tree
AM	a present tense of the verb be	
AN	a form of the indefinite article
AR	the letter "R"
AS	to that extent
AT	in the position of
AW	exclamation of disappointment
AX	(verb) to work on with an axe
AY	an affirmative vote (also AYE)
BA	the eternal spirit in egyptian mythology
BE	(verb) to exist
BI	a bisexual person
BO	Amer. slang for friend
BY	near; a side issue (pl. BYS)
CH	English dial. for I
DA	a Burmese heavy knife
DE	preposition meaning of or from, in names
DI	a plural of deus (a god)
DO	(verb) to achieve; a celebration (pl. DOS)
EA	a river (dial.)
ED	educational
EE	Scots. dial. for eye (pl. EEN)
EF	the letter "F"
EH	(verb) to say "Eh" for surprise etc
EL	an elevated railway
EM	a printer's measure
EN	a printer's measure, half of an EM
ER	an expression of hesitation
ES+	the letter "S"
ET	a past tense of eat
EX+	the letter "X"
FA	a musical note
FY	an interj. expressing disgust (also FIE)
GI	a judo or karate costume
GO	(verb) to depart; a Japanese board game (pl. GOS)
GU	a simple violin used in Shetland (alos GJU, GUE)
HA	an exclamation of surprise
HE	a male
HI	an exclamation of greeting
HM	interj. expressing thoughtful consideration
HO	intej. calling attention
ID	part of the psyche
IF	a condition
IN	(verb) to harvest
IO	a cry of joy
IS	a present tense of be
IT	impersonal pronoun
JO+	a sweetheart
KA	(verb) to serve (also KAE)
KO	a Maori digging stick
KY	cows (also KYE) 
LA	a musical note
LI	a Chinese distance unit
LO	look, behold
MA	mother
ME	a musical note (also MI)
MI	same as ME, above
MM	exclamation of satisfaction
MO	a moment
MU	a Greek letter
MY	belonging to me
NA      interj. of disbelief
NE	arch. form of not
NO	a no vote (pl. also NOES)
NU	a Greek letter
NY+	(verb) to approach (pl. also NYS)
OB	an objection
OD	a mystic universal force
OE	a grandchild in Scotland (also OY, OYE)
OF	belonging to
OH	(verb) to exclaim "Oh" for surprise
OI	interj. calling attention
OM	a syllable intoned as part of a mantra
ON	to go on
OO	wool (Scots.)
OP	an abstract art style
OR	the heraldic colour gold
OS+	a bone
OU	interj. expressing concession
OW	interj. expressing pain
OX+	a mammal with hooves
OY	same as OE, above
PA	father
PE	a Hebrew letter (also PEH)
PH	a measure of acidity
PI	(verb) to jumble or disorder (pr.p. PIEING, PIING)
PO	a chamber pot
QI	a Chinese life force
RE	a musical note
SH	interj. requesting silence
SI	a musical note
SO	a musical note (also SOH)
ST	an exclamation of impatience
TA  	thanks
TE	a musical note
TI	a small tree
TO	as far as
UG	(verb) to cause hatred
UH	interj. expressing disbelief
UM	interj. of hesitation
UN	one
UP	(verb) to increase
UR	interj. expressing hesitation
US	a third person pronoun
UT	a musical note
WE	a third person pronoun
WO	a curse
XI	a Greek letter
XU	a Vietnamese coin (pl. XU)	
YA	you
YE	you
YO	a call for effort
YU	precious jade
ZO	a Himalayan cross between a yak and a cow (also DZO, DSO, ZHO, DZHO)