1. The odd word out is fun. The rest of the words (dull, tiring, awful) are negative adjectives, while "fun" is a positive adjective.
2. The odd word out is painting. The rest of the words (dominoes, backgammon, billiards) are games.
3. The odd word out is bad. The rest of the words (good, fond, keen) are positive adjectives, while "bad" is a negative adjective.
4. The odd word out is always. The rest of the words (rarely, quick, never) are adverbs of frequency, while "always" is an adverb of frequency that expresses a high frequency.