break or vacation

(やすみ) Could be anything from a short break to summer vacation – it all depends on the word before it.   $$$
(きゅうけい) Break at work (昼休み is actually a type of きゅうけい) OR break from studying/training. Just long enough to eat some food and stretch – usually 15 minutes to an hour.
(きゅうじつ) A holiday – Christmas, Arbor Day, etc.
(きゅうか) Long vacation from work (maternity leave, 2-week vacation to Barbados, etc.)