Answer: CEN
CEN is a crossword puzzle answer that we have spotted 45 times.
    - Midmost: Abbr.
 
    - Mid.
 
    - The 21st, e.g.: Abbr.
 
    - The 1900's, e.g.: Abbr.
 
    - The 1000's, e.g.: Abbr.
 
    - 100 yrs.
 
    - The 900's, e.g.: Abbr.
 
    - Fivescore yrs.
 
    - Long time: Abbr.
 
    - 1776-1876: Abbr.
 
    - What few people live for: Abbr.
 
    - 100 years: Abbr.
 
    - Many yrs.
 
    - Part of a millennium (abbr.)
 
    - Life span of many a tortoise (abbr.)
 
    - A new one comes every 100 yrs.
 
    - 1900-99, e.g.: Abbr.
 
    - About 877,000 hrs.
 
    - Decimal meas.
 
    - 20th, e.g.: Abbr.
 
    - 100-yr. period
 
    - Five score yrs.
 
    - 100-year time span (Abbr.)
 
    - 1200 mos.
 
    - One ended in 2000: Abbr.
 
    - 1900s, e.g.: Abbr.
 
    - 100-yr. span
 
    - Millennium div.
 
    - 100-yr. timespan
 
    - Div. of a millennium
 
    - Period of 100 yrs.
 
    - 2000s, e.g.: Abbr.
 
    - Time line period: Abbr.
 
    - 100-yr. stretch
 
    - 21st, e.g.: Abbr.
 
    - 5 scores
 
    - Noted arcade classic, and this puzzle's theme
 
    - 800s, e.g.: Abbr.
 
    - One-tenth of a millennium (abbr.)
 
    - In the middle: abbr.
 
    - Historic span: Abbr.
 
    - The 2000s, e.g.: Abbr.
 
    - Long life: Abbr.
 
    - One of 10 in a millennium: Abbr.
 
    - The 1900s, e.g.: Abbr.