1. What do the following words have in common?

TIMES
TOWN
MEAL
DANCE
FOUR

2. What do the following numbers have in common?

200
600
1001
1050
1100
1500

Answers:

1. Each word can be preceded or followed by SQUARE. 

2. Each number, in Roman Numerals, is a familiar abbreviation: 

200 - CC (cubic centimeter)
600 -  DC
1001 - MI (Michigan)
1050 - ML (milliliter)
1100 - MC (emcee)
1500 - MD

Credit: NY Times Crossword - Aug. 18, 1985
Charles M. Deber
WHEN IN ROME  (adapted)

1500 - MD