Answer:

aves

Answer	Crossword Clue
AVES	Flying class?
AVES	Class of fliers?
AVES	Madison and Fifth in Manhattan: Abbr.

AVES	D.C.'s New York and Pennsylvania
AVES	Class of birds
AVES	Greetings of old
AVES	Streets: Abbr.
AVES	Some Monopoly purchases: Abbr.
AVES	Many Monopoly properties: Abbr.
AVES	Some Monopoly properties: Abbr.
AVES	Upper class?

AVES	Forum greetings
AVES	Greetings of long ago
AVES	Bird classification
AVES	Pennsylvania and others: Abbr.
AVES	Map parts: Abbr.
AVES	Fifth and Mad.
AVES	Mad. and Lex.
AVES	They sometimes have presidents' names: Abbr.

AVES	Welcomes
AVES	Prayers to Mary
AVES	Class that's for the birds
AVES	Ancient greetings
AVES	17 Monopoly props.
AVES	St. crossers
AVES	Former ova
AVES	Lexington and Madison: Abbr.