Answer:

aptno

Answer	Crossword Clue
APTNO	Part of a housing-unit addr.
APTNO	Part of many an N.Y.C. address
APTNO	10-G, e.g.: Abbr.

APTNO	City address abbr.
APTNO	Metropolitan address abbr.
APTNO	Abbr. in many an urban address

Crossword

a puzzle consisting of a grid of squares and blanks into which words crossing vertically and horizontally are written according to clues.