Chi

Human-Computer Interaction, otherwise known as Computer-Human Interaction (CHI)

Chromosomal crossover, in homologous recombination, a viral DNA sequence called a "crossover hotspot instigator" (CHI)

Chi (letter), the Greek letter, Χ

Chi (kana), a letter used in the Japanese language Hiragana

Qi (also spelled Ch'i; traditional: 氣, simplified: 气), the word roughly meaning "life energy" and written qì in Pinyin