2-Letter Words with Definitions

Bold indicates word cannot be extended with "S'
Plus sign (+) indicates word can be extended by "ES'

AA	rough jagged lava found in Hawaiian volcanos
AB	an abdominal muscle
AD	short form of advertisement
AE	one (Scots.)
AG+      agriculture
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+	as in ifs and ans, things that might have happened, but which did not [adj]
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	education
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
FE	a Hebrew letter
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 (also GJU, GUE)
HA+	an exclamation of surprise
HE	a male
HI+	an exclamation of greeting
HM	interj. expressing thoughtful consideration
HO+	interj. 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
JA	yes
JO+	a sweetheart
KA+	(verb) to serve (also KAE)
KI	the spirit of Japanese martial art, see QI
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	a NZ bird, petrel
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	a bloke
OW+	interj. expressing pain
OX+	a mammal with hooves
OY+	same as OE, above
PA	father
PE+	a Hebrew letter (also PEH)
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
ZA	contraction of "pizza"
ZO	a Himalayan cross between a yak and a cow (also DZO, DSO, ZHO, DZHO)